We examined seasonal variation in fish species composition in coastal waters near Wolseong Nuclear Power Plant in the East Sea of Korea. A total of 72 species, 39 families, 14 orders, 46,214 individuals, and 4,639,667 g were collected. Glyptocephalus stelleri was the most dominant species by number of individuals (35%), followed by Clupea pallasii (26%). Liparis tanakai and Lophius litulon were the dominant species by biomass, accounting for 46% and 28%, respectively. We showed that bottom salinity and temperature are the most important environmental factors influencing fish species composition. Although bottom salinity did not differ statistically among seasons or stations, we detected some variation among stations. Additionally, bottom temperature differed among seasons and stations (P<0.05), affecting numbers of individuals and biomass. Thus, seasonal variation in fish assemblages can be classified into two groups: spring/summer and autumn/winter.