This study reports results of a 14-month live-trap study of small-rodent communities in 2 habitats, cloud forest and disturbed areas, at Las Joyas Scientific Station of the Sierra de Manantlán Biosphere Reserve, western Mexico. Seven taxa of 2 families (Muridae, Heteromyidae) of small rodents were captured (Hodomys alleni, Liomys pictus, Oryzomys couesi, Peromyscus aztecus, Reithrodontomys fulvescens, R. sumichrasti, and Sigmodon alleni). Information about age structure, population dynamics, biomass, and reproduction were obtained with mark–recapture techniques for the most abundant species (P. aztecus and R. fulvescens) in both habitats. These species comprised 80.3% of the 707 captures in the cloud forest (P. aztecus, 51.2%; R. fulvescens, 29.1%), whereas, in the disturbed areas, R. fulvescens represented 81.7% of the 916 captures. Species varied in population density, relative abundance, and timing of reproduction, which was seasonal. Reproductive activity for P. aztecus peaked in the middle of the wet season (September 1995) in the cloud forest and in the wet season and middle of the dry-cold season (January 1996) in the disturbed areas. R. fulvescens showed reproductive activity in the wet season (July–October 1995) in both habitats. Density fluctuated annually for P. aztecus in both habitats, with a peak in January and February 1996; R. fulvescens showed the same patterns of density in both habitats with the highest values at the end of the wet season.