Policy Planning Minister Keheliya Rambukwella said Ukraine would also overhaul four identical ground attack aircraft already with the island's airforce.
The four new planes will be delivered shortly to the airforce, which carries out regular air raids against Tamil rebels in the island's north and east.
The deal is worth 9.8 million dollars, according to press reports.
Rambukwella said he did not have price details for the second-hand, swing-wing MiGs, which will boost the airforce fleet of a handful of Israeli-built Kfir and Chinese-made F-7 ground attack aircraft.
"What we are paying to buy four used planes is less than what a friendly country quoted for the refurbishment of four (existing) planes," Rambukwella said.
Sri Lanka's airforce resumed air attacks against the Liberation Tigers of Tamil Eelam in April after the guerrillas were blamed for a suicide assassination attempt on army chief Sarath Fonseka.
Kfir and MiG-27 aircraft have been bombing suspected T