This study aims to explore the effects of landscape type and human disturbance level on the composition and activity frequency of forest mammals in Taiwan’s low- to mid-altitude areas. The study areas are the Lienhuachih Experimental Forest in the mosaic landscape of central Taiwan and the Fushan Experimental Forest in the continuous natural forest in the northeast. From February 2023 to March 2024, 20 sampling sites were set up in the two forest areas for infrared automatic camera monitoring, and the occurrence frequency (Occurrence Index [OI]) and species composition, as well as the seasonal changes in species OI values, were analyzed. During the study period, a total of 17,931 mammal images were recorded, and a total of 15 species of wild mammals from five orders and 10 families were confirmed. Non-parametric two-way ANOVA showed that the OI values of eight common mammals were significantly different among regions. Sus scrofa taivanus, Paguma larvata, and Callosciurus erythraeus thaiwanensis had higher OI values in Lienhuachih, indicating that these animals preferred the mosaic landscape of Lienhuachih. In addition, Prionailurus bengalensis with conservation values was only recorded in Lienhuachih, indicating that the area had critical habitat potential. Forest species, such as Muntiacus reevesi micrurus, Capricornis swinhoe, Macaca cyclopis, and Melogale subaurantiaca had significantly higher OI values in Fushan, indicating the importance of continuous natural forests for these species. Some species showed heterogeneous responses to human disturbance, such as Cal. erythraeus thaiwanensis preferring high-disturbance environments, while S. scrofa taivanus tended to use low-disturbance areas. Most species showed no obvious seasonal activity changes; only Mel. subaurantiaca in Lienhuachih had significant different OI values between seasons (summer and autumn). During the study period, Martes flavigula chrysospila and Rusa unicolor swinhoii were recorded for the first time in Fushan, indicating that the species at higher altitudes had the potential to spread to medium and low altitudes, and their ecological impacts deserve attention. Overall, this study pointed out that landscape type and degree of disturbance have a significant impact on the species composition and habitat use of mammals. Future conservation strategies should consider the different ecological needs of species, combine long-term monitoring and habitat management, and improve the habitat sustainability and biodiversity protection of low- to mid-altitude forest mammals.