The growth of young-of-the-year blue spot mudskipper, Boleophthalmus pectinirostris, was investigated using length-frequency data for 395 individuals collected from a mud flat in southwestern Korea between August and October 2001. Three cohorts were separated by the Bhattacharya method. In October, individuals of cohort-I reached 98 mm in total length, whereas those of cohort-III reached just 66 mm. Each cohort reached hibernation in November, that could be related to the ring formation in the following year.