Genetic diversity and gene flow patterns in Pollicipes mitella were investigated with a nucleotide sequence analysis of 514 base pairs from the mitochondrial cytochrome c oxidase subunit I gene (COI) in 124 samples collected from six Korean populations. In total, 59 haplotypes were defined by 40 variable nucleotide sites in the COI region. The haplotypes had shallow haplotype genealogy and no geographic associations. All populations had high haplotype diversity (0.909 to 0.979) and low nucleotide diversity (0.0055 to 0.0098). The haplotypes with recently diverged nucleotides were distributed by long-range larvae dispersal among regional populations. The pairwise fixation indices ($F_{ST}$) estimated with the exact test and migration rates indicate that substantial gene flow has occurred among populations as a result of sea currents, except between the Uljin (East Sea coast) and other Korean populations. This suggests that significant genetic differentiation and low migration rates have affected the Uljin population.