"Our government will release 56 political prisoners," presidential adviser Hla Maung Shwe told AFP, in comments confirmed by correctional department officials.
Setting free dissidents detained arbitrarily under the former junta has been a cornerstone of reforms by a new quasi-civilian regime and has been warmly welcomed by the international community with the scrapping of most western sanctions.
Hundreds of political detainees have been freed since President Thein Sein took power in March 2011.
Thein Sein, who travelled today to a meeting of regional powers in Brunei, announced there would be "no prisoners of conscience in Myanmar" by the end of the year during his first visit to London in July.
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Numbers for political prisoners held in Myanmar vary, but Aung San Suu Kyi's opposition party said there were around 140 activists held before today's announcement.
Thet Oo, from the ex-detainees group Former Political Prisoners, told AFP that he could confirm that some of the 56 had already been set free, adding that his organisation estimates that around 50 new activists have been held by the current regime.
The arbitrary imprisonment of political opponents was a hallmark of the previous brutal junta and sparked a web of western sanctions which stifled the economy.
Since Thein Sein took power, the nation has undergone dramatic change including the election of opposition leader Suu Kyi to parliament.
Myanmar analyst Richard Horsey said the government were still arresting and detaining activists, but said this was "generally in a transparent way unlike the past".
"So the key will be, at the end of the year, has Thein Sein met his pledge on having no political prisoners, and how are the more recently arrested people classified?" he said.