U Htin Kyaw, 72, was elected as the president in March, 2016, after Aung San Suu Kyi's National League for Democracy (NLD) won the 2015 general election.
Under the constitution, the presidential vacancy will be filled within seven days through the parliament.
YANGON, March 21 (Xinhua) -- Myanmar's First Vice President U Myint Swe will serve as acting president according to the constitution until the parliament re-elects the new president, U Zaw Htay, director-general of the President Office, told Xinhua on Wednesday following U Htin Kyaw's resignation.
U Zaw Htay added that the resigned president U Htin Kyaw underwent medical treatment in Singapore in January and insisted on his resignation.
The President's Office earlier on Wednesday released an official statement of President U Htin Kyaw's resignation, citing health as the reason.