Bank of Ayudhya Public Company Limited, branded and commonly referred to as Krungsri (sometimes stylized as krungsri), is the fifth-largest bank in Thailand in terms of assets, loans, and deposits, and one of Thailand’s six Domestic Systemically Important Banks (D-SIBs). Krungsri is a member of the Mitsubishi UFJ Financial Group.

The Bank of Ayudhya was established on 27 January 1945 in Phra Nakhon Si Ayutthaya Province, the former capital of the Kingdom of Siam until the city's destruction in 1767. The bank opened its doors on April 1, 1945, with registered capital of one million baht.

In 1970, the bank's head office was relocated to Ploenchit Road, coinciding with the bank's receiving a royal warrant of appointment and garuda emblem from King Bhumibol Adulyadej on 15 May 1970. The bank was listed on the Stock Exchange of Thailand on 26 September 1977, trading symbol, "BAY".

On 3 January 2007, Krungsri and GE Capital became strategic partners. GE Capital and Ratanarak Group were major shareholders with a 33 percent and a 25 percent stake in BAY, respectively.

In September 2012, GE announced the sale of 7.6 percent of its stake in Krungsri via a number of block trades, reducing their ownership to 25.33 percent.

After having undergone changes in the late 2000s, including the acquisition of GE Money Thailand, and Bank of Ayudhya unified its subsidiaries and rebranded. In 2014, the bank rebranded as "Krungsri" (shortened from กรุงศรีอยุธยา, "capital city/revered city Ayutthaya"), the bank's formal name and use tagline Make Life Simple. In the media, the formal and colloquial names are used interchangeably, while for the bank's own marketing (such as logos, URL, storefronts, ATMs, bank cards and promotional material) "Krungsri" is used.

In February 2023, Krungsri launched its brand refresh and updated Thai slogan of “Make Life Simple” (“ชีวิตง่าย ได้ทุกวัน”).

Bank of Ayudhya's investments in subsidiaries, associates and joint ventures net as of 31 December 2016 and 2015.