Genetic variation among populations of Gekko hokouensis from Kyushu, and the northern and the central Ryukyus was investigated by use of protein electrophoresis. From the results, the following three groups were recognized: Group 1, consisting of populations of Kyushu except for that of the southwestern part; Group 2, consisting of populations of southwestern Kyushu and the northern Ryukyus; and Group 3, consisting of populations of the central Ryukyus. Samples belonging to the Group 2 were genetically fairly uniform with low heterozygosities despite their wide geographic range that includes both the Oriental and Palearctic faunal regions delimited by the Tokara Tectonic Straits. This strongly suggests that the populations composing this group have spread over their current range recently. In addition, the degree of genetic differentiation between populations of the Groups 1 and 2 and the Group 3 (Nei's D: 0.083-0.175, x̄ = 0.129) was too small to have resulted merely from the deduced geographic isolation between the northern Ryukyu-Kyushu region and the central Ryukyus. This suggests that at least one of those two groups has colonized after formation of the Tokara Tectonic Straits by secondary dispersals. Circumstantial evidences seem to favor the secondary dispersals of the northern Ryukyu-Kyushu groups. Data for geographic patterns of allelic distributions and of intrapopulational genetic variabilities suggest that the southern Kyushu populations have received gene flow also from an extralimital source as well.