Effects of substratum, its submersion season, and submersion period on the development of subtidal fouling assemblages were examined for a period of 18 mo in a subtropical harbor. Four types of artificial surfaces, including steel, stainless steel, cathodically protected steel, and concrete, were initially submersed in fall and spring, respectively, and sampled every 3-6 mo. There is little evidence that type of substratum influenced the development of fouling assemblages. However, richer taxa and greater biomass of fouling assemblages occurred on spring-than on fall-submersed plates. Fouling biomass reached a maximum at the end of the study period, but the taxa were richest at the end of 12 months. Classification and ordination analyses show that the species compositions of fouling assemblages were structured by submersion season and submersion period of the substratum, but not by the nature of the substratum itself. The oyster, Crassostrea gigas, dominated spring plates throughout the study period, but the assemblages on fall plates were highly variable. This indicates that submersion season and submersion period of the substratum are more important than type of substratum in the development of subtidal fouling assemblages. However, the abundance and species composition on spring and fall plates became less dissimilar by the end of 12 mo. This suggests that development takes the same course even with different seasons of submersion. It is likely that the fouling species acted in individualistic manners, and the assemblages were composed simply of fouling species which arrived at that time. Our results demonstrate that the developmental process is greatly affected by seasonal fluctuations in larval abundance and historical components on a substratum.