Based on samples collected in 1989–90, I report on several aspects of the natural history of species of small mammals from seasonal montane areas in subtropical central Taiwan, including their reproduction, demography, sex ratio and body size. The climatic seasonality in the areas is striking. The wet season lasts from May through September and the dry season from October through April. The phenology of plant life is related to this seasonality: vegetative growth occurs primarily in the wet season, but fruit and seed production is concentrated in the dry season. Variation in the reproduction and demography are analysed between the wet and the dry season for six species, Apodemus semotus, Niviventer culturatus. Eothenomys melanogaster, Microtus Kikuchii, Anourosorex syuamipes and Soriculus fumidus. Two murid rodents. A semotus and N. culturatus. are capable of breeding year-round, whereas the microtine rodents, E. melanogaster and M. Kikuchii, have discrete breeding seasons. The shrews, A. squamipes and S. fumidus are both seasonal breeders. but they differ in the timing of their breeding cycles. While S. fumidus breeds primarily in the late dry season, A. syuamipes reproduces in the wet season. Finally, seasonal variation in reproduction is discussed in relation to phylogenetic and physio-ecological characteristics of these six species.