A bimonthly study of the spatial variations in fish assemblages in the six mangrove creeks along the western coast of Taiwan was conducted from February 1996 to February 1997. Fyke nets were used to collect fishes in each of three creeks in the north (subtropical) and south (tropical) regions. A total of 79 fish species belonging to 33 families were collected and, of these, the Gobiidae, Mugilidae, Leiognathidae, and Cichlidae were the most diverse families. The fish assemblages in each creek were dominated by a small number of small fishes, most of which are the young of commercially important species. Their life cycles occurred to some extent in estuarine environments. Analyses by classification and ordination separated the assemblages into a northern group and a southern group and showed that the assemblages were far more temporally varied in the southern creeks than in the northern creeks. Fifty fish species were recorded in the northern creeks and 49 fish species in the southern creeks, with 20 species present in both regions. No significant difference in number of species per netting was detected between the regions. The number of individuals and biomass per netting were greater in the northern creeks than in the southern creeks. Rainfall and organic content of sediments may be responsible for the difference in fish abundance between the regions. In the northern creeks the assemblages were dominated by Liza macrolepis and Liza affinis in winter and spring, but the assemblages were more diverse in summer and fall. In the southern creeks, the assemblages were always characterized by several species and their dominance varied from month to month. The differences in the assemblage structure in northern and southern mangrove creeks are likely due to the oceanic current patterns around Taiwan.