The mason bee (Osmia cornifrons Radoszkowsky) is an excellent pollinator of apple. To understand geographic genetic variation of the species and relationships among populations sequenced a portion of mitochondrial COI gene, which corresponds to “DNA Barcode” region (658 bp) from 81 individuals collected over eight localities in Korea. The sequence data were used to investigate genetic diversity within populations and species, geographic variation within species, phylogeographic relationship among populations, and phylogenetic relationship among haplotypes. Summarized, overall moderate to low genetic diversity within populations and species was characteristic, concordant with the high potential to disperse of O. cornifrons in Korea. Although two populations were genetically subdivided from the remaining localities, no clear regional bias was observed. Overall, high rate of gene flow among localities and low FST was characteristic considering other relevant studies that investigated population genetic structure of other insects occurring in Korean peninsula.