The Ministry of Defense completed construction of Don Mueang Airfield, which in time would become Bangkok International Airport, in 1914. In the early years most of the country’s aviation-related activities were conducted by and under the supervision of the Ministry of Defense. The history of civil aviation in Thailand began in 1940, when the Royal Thai Air Force established the Civil Aviation Division to oversee international air travel. Upgraded to the Directorate of Civil Aviation in 1948, it was assigned responsibility for overseeing all activities at the airport.

In 1979, the National Law Council, acting on orders from the Parliament, drafted the Airports Authority of Thailand Act (B.E.2522), which provided for the establishment of the Airports Authority of Thailand (AAT), a state enterprise under the Ministry of Transport, on March 3, 1979. Responsible for all airport operations and airport-related businesses, the AAT was subject to Cabinet authority and Ministerial regulations. The new organization, tasked with promoting the development of the country’s aviation industry and other related services, first took up its duties at Bangkok International Airport on July 1, 1979. Subsequently, Airports Authority of Thailand assumed responsibility for five additional international airports: Chiang Mai (March 1988), Hat Yai (August 1988), Phuket (October 1988), Suvarnabhumi (June 1993), and Chiang Rai (October 1998).

Airports Authority of Thailand set up the New Bangkok International Airport Company (NBIA) on February 27, 1996, to oversee the construction of the new Suvarnabhumi Airport. Jointly owned by Airports Authority of Thailand and the Ministry of Transport, the new company was in charge of airport construction from 1996 to 2006.

On September 30, 2002, AAT, a state enterprise created under the Airports Authority of Thailand Act, became a public limited company named “Airports of Thailand Public Company Limited ” or AOT, in compliance with the State Enterprise Capitalization Act B.E. (1999). The newly formed company had registered capital totaling 5.747 billion Baht, divided into 574,700,000 ordinary shares each with a par value of 10 Baht, all owned by the Ministry of Transport. As of the official date of its founding, AOT took possession of all businesses, rights, liabilities, responsibilities, assets (with the exception of land measuring approximately 487 rai 1 ngan 55 square wah near Bangkok International Airport) and staff formerly belonging to the Airports Authority of Thailand. This allowed the company to carry on the work of supervising the national airports without interruption. The Royal Decree Defining the Authority, Rights and Benefits of Airports of Thailand Public Company Limited B.E.2545 (2002) stipulates that AOT entitle to the following powers, exemptions, privileges and protections accorded under the Airports of Thailand Act and other laws relating to the Airports of Thailand, with these exceptions:

1. AOT assets essential to the aviation business which generate public benefits are not subject to legal liability;
2. Only AOT personnel and employees appointed by the Minister to serve as law enforcement officers under the Criminal Code and as administrative personnel or high-ranking police officers under the Code of Criminal Procedure are authorized to maintain security within the airport grounds.

On August 4, 2003, the Ministry of Transport, as AOT’s sole shareholder, decided to raise AOT’s registered capital from 5.747 billion Baht to 10 billion Baht through the issue and sale of an additional 425,300,000 ordinary shares with a par value of 10 Baht each to the Ministry of Finance. The purchase was effected through the Finance Ministry’s transfer of 42,530,000 shares of stock in the New Bangkok International Airport Company Limited with a face value of 100 Baht per share. As a result, AOT’s registered capital rose by 4.253 billion Baht to 10 billion Baht, divided into 1 billion ordinary shares with a par value of 10 Baht each, and the company took control of 99.9% of the shares in the New Bangkok International Airport Company Limited. Then on January 30, 2004, the Securities and Exchange Commission gave AOT permission to offer shares of stock to the general public through the Stock Exchange of Thailand. On February 9, AOT made 16 million ordinary shares available to its staff and to staff at the New Bangkok International Airport Company at the face value of 10 Baht per share, and on March 9 and April 8, 2004, the company offered an additional 358.8 million shares to the general public and 53.77 million shares to foreign financial institutions, At 42 Baht per share, the public offering raised 4.2857 billion Baht, with surplus value totaling 13,202.24 billion Baht and sales expenses amounting to 634.58 million Baht. As of September 30, 2004, AOT’s fully-paid shares totaled 1,428,570,000, with a par value of 10 Baht per share, and net surplus value of 12,567,660,000 Baht. The company’s major shareholder is the Ministry of Finance, which controls approximately 70% of total shares.

On September 10, 2002, the Cabinet approved the transfer of business, assets, rights, liabilities, responsibilities and staff from the New Bangkok International Airport Company to AOT once construction of Suvarnabhumi Airport was completed and prior to its official opening. At this time NBIA would cease to exist as an independent company but would become part of AOT. This was carried out on January 1, 2006, and with the approval of the Ministry of Finance and Ministry of Social Development and Human Security, a Cabinet resolution acknowledging the transfer was passed on February 28. NBIA staff was transferred to AOT on December 8, 2004, and the transfer of assets, rights, liabilities and obligations was completed on January 1, 2006. The book value of assets and liabilities appearing in NBIA’s books as of December 31, 2005, was 100,913.28 million Baht (consisting of during construction assets valued at 91,82025 million Baht, land and buildings worth 149.35 million Baht, and other items valued at 8,943.68 million Baht) and 62,429.47 million Baht, respectively. As for the differential of 38,483.81 million Baht, AOT issued NBIA promissory notes with an annual fixed interest rate of 0.5% which were set to mature on the last working day prior to NBIA’s handover of any remaining investment money. NBIA was officially closed down on July 31, 2006, subsequent to two extraordinary shareholders meetings which took place on July 12 and July 28, 2006. At present the company is in the process of liquidation, and no interest has accrued on the promissory notes since NBIA closed down.