Information about factors influencing forest-floor small mammals of midwestern riparian forests in agriculture-dominated areas is necessary for improved forest management. We determined occurrence and capture rates of forest-floor small mammal taxa at 4 northeastern Missouri riparian forests during 1995–2002. We modeled the effects of year, study site, and precipitation (flooding) on relative abundance of commonly captured taxa. We also evaluated changes in the species assemblage and capture rates resulting from silvicultural treatments (clearcut, basal area retention, and unharvested) at a 215-ha forest tract. We captured 12 taxa of forest-floor small mammals, of which 10 were captured at all sites. The species assemblages were dominated by habitat generalists, such as Peromyscus spp. and Sorex spp. Among-year variation in capture rates was large for all common taxa. Precipitation amounts during spring and summer were negatively correlated with relative abundances of several forest-floor small mammal taxa. We measured few changes in taxonomic composition or abundances of forest-floor small mammals in response to silvicultural treatments. There was some indication that Peromyscus spp. and short-tailed shrew (Blarina brevicauda) abundance decreased in areas where treatments increased fragmentation, but among-year differences accounted for more variation than treatment effects. We suggest that small mammal assemblages in fragmented midwestern riparian forests are dominated by habitat generalists and their abundances are primarily affected by variability in environmental conditions (especially flooding during the breeding season). Silvicultural treatments may have minimal effects on taxonomic composition or abundance, as long as forests are allowed to regenerate, mature forest blocks are maintained, and other important factors (e.g., hydrology) are not altered.