The announcement came a few days before US President Barack Obama arrives in Myanmar on a state visit as part of a four-day Asian trip from November 17-20.
In the past year under the new government dispensation, Thein Sein had granted hundreds of prisoners amnesty
as part of democratic reforms being initiated by the post martial law regime.
For decades, Myanmar has been under military rule which isolated the Asian country from the rest of the western world.
Myanmar's democracy leader Aung San Suu Kyi, who was jailed in the 1990's for over 15 years by Myanmar's military junta for advocating democratic reforms, has been credited with the easing of economic sanctions by western countries including the US and a number of European nations.
Suu Kyi, who was elected to the new parliament of Myanmar after her release from jail had traveled to the US and Europe to drum up support for Myanmar's fledgling democracy. Her foreign goodwill trips were followed by Thein Sein's diplomatic visits to these countries which resulted in the restoration of diplomatic ties.
Obama has been criticized for choosing Myanmar as his first country to visit after being elected for the second term. BBC's Jonathan Head in Bangkok
says "it is too soon to reward the government for reforms which have just started."
Some opposition groups have criticized Thein Sein for using "strategically timed prisoner releases to appease the international community."
"The release of prisoners of conscience should not be used as a bargaining chip," said Ko Ko Gyi, a leader of the country's 1988 pro-democracy uprising who spent many years in prison.
The last amnesty took place in September, a week before Thein Sein visited New York for the U.N. General Assembly, AP
Meanwhile, more people have been detained during protests where "military still acts with impunity in border areas where it is fighting ethnic insurgents", says the BBC