The Georgian parliament has approved the release of about 3000 prisoners and shorter terms for thousands more.
Georgia's previous government - backed by President Mikheil Saakashvili - was hit by a scandal over prisoner abuse.
The new government of Prime Minister Bidzina Ivanishvili, a political opponent of the president, says many inmates were imprisoned unfairly.
But Mr Saakashvili called the amnesty a "mass release of criminals", and warned of grave consequences.
The first prisoners are expected to be released later on Sunday.
A BBC correspondent in Tbilisi reports that some Georgians fear the move could mark a return to the crime-ridden 1990s and that many worry that powerful mafia bosses, who fled the country while the last government was in power, will come back if they think this new administration is soft on crime.