It was not immediately clear whether scores of political activists still languishing in Myanmar's jails would be among those freed, but the amnesty comes ahead of Obama's keenly-anticipated November 19 trip to the once army-ruled country.
"The announcement will be printed tomorrow in the state run newspaper," presidential office spokesman Zaw Htay said while a second official, requesting anonymity, said 450 prisoners would be released.
Myanmar has already freed hundreds of political prisoners locked up during decades of authoritarian rule as part of reforms responsible for a dramatic thaw in relations between the West and the long-isolated nation formerly called Burma.
The last major amnesty in September saw dozens of dissidents among more than 500 inmates pardoned from their sentences.
But many political prisoners still remain behind bars and opposition groups estimated around 300 activists were in jails around the country before the September amnesty.
Campaign group the Assistance Association for Political Prisoners put the current figure at 283 in a list posted on its website on October 31.
Obama, who was re-elected just under a fortnight ago, will meet democracy icon Aung San Suu Kyi and President Thein Sein on his brief visit, the first to the country by a sitting US president.
Right groups said September's amnesty was timed as a sweetener to the US government as it came just before a historic visit to the United Nations in New York by President Thein Sein.
But it also comes at a pivotal time for Myanmar with deadly communal violence between Buddhists and Muslims in western Rakhine State threatening to overshadow the changes that have taken place.
Clashes in that region have claimed 180 lives since June and forced more than 110,000, mainly Rohingya Muslims, into makeshift camps.
Obama will discuss the violence during his historic visit to the country, US Secretary of State Hillary Clinton said Wednesday in Perth.
Clinton, who will accompany Obama next week to Myanmar, said the unrest between Rohingya Muslims and Buddhists would "of course" feature in Obama's talks.
The US President will also deepen his support for the reform process launched by Myanmar's president, which has seen Suu Kyi, who had been under house arrest for years, become a member of parliament.
Washington restored diplomatic relations with Myanmar and ended sanctions on investment in July, while the former junta-ruled nation has offered foreign firms access to many markets which were firmly closed under authoritarian rule.
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