Taiwan localizes between the subtropical and the tropical regions in Asia Pacific with the Kuroshio Current passing along its east side. The differences in the structure and abundance of coastal macroalgae in relation to environmental variables were investigated by determining the temporal dynamics (2001-2003) of intertidal macroalgal abundance and structure in northern (Hermei), southern (Nanwan) and southeastern (Taitung) Taiwan and the islands around Taiwan (Hsio-lu-chiu in the southwest, Penghu in the west, and Green Island and Lan-yu Island in the southeast of Taiwan). One hundred and seventy-one species have been identified with rhodophytes as abundant species. Species richness (number), diversity (H’), and evenness (J’) showed site variation in the order of Nanwan = Hsio-lu-chiu > Green Island > Hermei > Taitung > Lan-yu Island > Penghu for species number and H’, and Lan-yu Island >> Hermei > Hsio-liu-chiu > Green Island > Penghu > Taitung for J’. Dry weight biomass was higher in Hermei and Hsio-liu-chiu. The data from hierarchical cluster analysis and nonmetric multidimensional scaling ordination of species similarities between different sampling times and the results of analysis of similarity (ANOSIM) showed that macroalgal assemblage is structured primarily by site and secondarily by year. There were three groups: 1. Hermei, 2. Hsio-liu-chiu and Green Island, and 3. Nanwan, Taitung, Lan-yu Island and Penghu. The species structure was different between 2001 and 2003, but similar between 2001 and 2002 and between 2002 and 2003. Less typhoon disturbance in 2002 may be one of the factors in explaining annual variability in intertidal macroalgal assemblage structure. The comparison of species compositions with environmental variables by BIO-ENV stepwise (BVSTEP) analysis shows that water temperature, salinity and precipitation are the abiotic variables which best explain the spatiotemporal dynamics of intertidal macroalgal abundance and structure around Taiwan. Cold winter temperature contributes to the distinction of Hermei (in the subtropical waters of northeastern Taiwan) from other sites localized in tropical waters. Precipitation and salinity are the factors affecting the seasonality of intertidal macroalgae in Taiwan. These results indicate that geographic difference in macroalgal assemblage structure in the intertidal regions around Taiwan can be attributable to temperature differences between subtropical and tropical waters in Taiwan. Salinity changes due to precipitation are considered as governing the seasonality of intertidal macroalgal assemblage structure in Taiwan.