Arsa Sarasin (Thai: อาสา สารสิน; born 26 May 1937) is a Thai diplomat and businessman who served as Principal Private Secretary to King Bhumibol Adulyadej until he retired in 2012.

He then moved to the United States, where he study High school at Wilbraham & Monson Academy and received a bachelor's degree from Boston University.

Then, around two to three years later from 1982 to 1985, he was Permanent Secretary of the Ministry of Foreign Affairs and from 1985 to 1988 he was appointed ambassador to the United States.

From 1999 to 2012, he was Principal Private Secretary to King Bhumibol Adulyadej, responsible for aiding the monarch in the exercise of his official duties and relations with the government.

[3] He has sat on the boards of the family-owned Thai Pure Drinks Company, as well as the Siam Cement Group, Charoen Pokphand Foods, Dusit International, and Bangkok Dusit Medical Services.