Bovine leukemia virus (BLV) is a widespread specific pathogen of cattle. Analysis of the pol viral gene polymorphism has been used to characterize the polymorphism of BLV isolates at stock-breeding farms in Russia and Ukraine. The fragments of the pol gene corresponding to the reverse transcriptase and integrase 494 and 233 bp in size, respectively, have been used for analysis. Phylogenetic analysis has revealed several variants of BLV clustered with a high bootstrap support in Russia and Ukraine. A new classification of BLV variants is suggested. Comparison of phylograms based on the polymorphism of the nucleotide sequences of the integrase and reverse transcriptase domains did not show topological conflicts. Therefore, recombination between BLV variants has not been found.