A study on the seasonal changes of the benthic macroinvertebrate community was performed on the intertidal rocky shores ao eastern coast of Cheju island and U-do throughout four seasons from october 1991 to August 1992. The macroinvertebrates were composed of 10 phyla, 18 classes, 39 orders, 94 families and 201 species. the number of speecies were 183 in summer, 147 in autumn, 138 in spring and 94 in winter, respectively. The total wpecies collected throuhout the study period were 193 species in U-do and 151 species in the eastern coast of Cheju Island. Nodilittorina exigua was the most dominant species in all seasons, followed by Monodonta neritoides in spring, autumn and winter, and pollicipes mitella in summer. U-do was higher in species diversity and richness and lower in evenness than the eastern coast. Species diversity and richness were higher in summer than any other seasons in lower intertidal zones. Community dominance indices, however, were significantly higher in upper intertidal zones than in lower intertidal zones.