Milinkevich had been sentenced to jail for taking part in an unauthorized antigovernment protest on April 26, the 20th anniversary of the Chornobyl nuclear disaster.
Milinkevich ran against President Alyaksandr Lukashenka in elections in March condemned as fraudulent by the opposition and Western governments.
Lukashenka's reelection triggered unprecedented protests in Belarus. Hundreds of opposition supporters were jailed for taking part in the protests.
Two other opposition politicians, Alyaksandr Bukhvostau and Zmitser Dashkevich, were also released today. They had been jailed for taking part in the same protest rally two weeks ago.
(Belapan, AFP, AP)
MEET THE CANDIDATES: Read brief biographies of the four candidates in the March 19 election.