Partial sequence of the mitochondrial cytochrome b gene was analyzed to investigate genetic variation from 10 geographic populations of Granulilittorina exigua in Korea. The sequence of 282 base pairs was determined by PCR-directed silver sequencing method. The sequences of two species within the genus Littorina reserved in NIH blast search were utilized to determine geographic variations of species referred. The levels of mtDNA sequence differences were 0.00-2.54% within populations and 0.71-4.43% between populations. There were four amino acid differences between representative species of the genera Granulilittorina and Littorina, but no differences within populations of the genus Granulilittorina. The UPGMA and the N-J trees based on Tamura-Nei genetic distance matrix were constructed, which showed that the genus Granulilittorina was divided into three groups such as eastern (even exception for Tokdo population), southern, and western regional populations. The degrees of genetic divergence within populations of each group were p=0.021, p=0.019, and p=0.018, respectively. The divergence between the eastern and southern populations was p=0.032, showing closer relationship than with the western populations (p=0.052). Based on the diverged time estimation, the eastern and southern populations of Granulilittorina exigua in Korea diverged from the western populations about 2.1 MYBP, and the eastern and southern populations diverged from each other about 1.3 MYBP.