Sanan Devahastin na Ayudhya (also spelled Thephasadin among other variants; Thai: ????? ????????? ? ??????, RTGS: Sanan Thep-hatsadin Na Ayutthaya, IPA: [sà.nàn t?ê?p.hàt.sà.din ná? ?à.jút.t?á.ja?]; 1 January 1877 – 1 February 1943), better known by his noble title Chaophraya Thammasakmontri (????????????????????????, IPA: [t??â?w.p?rá.ja? t?am.má.sàk.mon.tri?]), was an educator, writer and senior government officer of Siam/Thailand.
He served as Minister of Public Instruction from 1915–1926, and was the first President of the National Assembly, serving during 28 June – 1 September 1932 and 15 December 1933 – 26 February 1934.