The mitochondrial cytochrome oxidase subunit I (COI) sequences of 610bp were determined for seven species of the genus Osmia from Korea and two species of outgroups. The sequences were extremely rich in A+T (75.1% on the average), especially in the third codon position. The transversion transition ratio was >1 and most transversions were occurred between A and T. The sequence divergence in pairwise comparisons among seven Osmia species ranged from 6% to 26%. The phylogenetic trees estimated from the nine sequences through PAUP and PHYLIP analyses formed two clades, which was supported by high bootstrap values of both analyses. The phylogenetic trees, appeared to conform most satisfactorily with the traditional views of taxonomic relationships within this group of Osmia mason bees, were produced. There was no difference between Korean and Japanese O. cornifrons (Radoszkowsi) and O. taurus Smith in COI sequences used this study.