The legislation approved yesterday may also help reduce overcrowding in the Central American country's prisons.
The government has said it is studying a series of measures to improve the fight against violent Mara street gangs.
The measure approved yesterday will allow the release of inmates with a terminal or degenerative illness and prisoners over age 60 who have served at least a third of their sentences.
Nobody with a sentence of over eight years nor those convicted of serious offenses will be eligible under the measure, which is scheduled to last one year.