Abstract: We investigated the biofouling communities on concrete and steel reefs in Daya Bay, Shenzhen, in May, July, October and December, 2008. Seasonal variation of species composition of biofouling communities was significant.On concrete reefs, 60 species were found in autumn, 58 in summer, 56 in spring and 37 in winter; only 23 species were found simultaneously in four seasons. The descending order of biomass of biofouling communities was winter>autumn>spring>summer. No significant difference in seasonal species dominance was found. The index of richness (R) was autumn>summer>spring>winter; the index of Shannon-Wiener (H′) was summer>autumn>spring>winter; the index of evenness (E) was summer>autumn>spring>winter. On steel reefs, 70 species were found in spring, 57 in summer, 51 in autumn and 41 in winter; only 17 species were found simultaneously in four seasons. The biomass of biofouling communities was spring>autumn>summer>winter. No significant difference in seasonal species dominance (Y) was found. The R value was spring>summer>winter>autumn; the H′ value was winter>summer>autumn>spring; the E value was winter>summer>autumn>spring. However, no significant difference in R, H′ and E values was found, neither was biofouling communities between concrete and steel reefs.