The distribution and status of bats in eastern Montana remain poorly documented, and the value of riparian corridors in Montana to bats has not been quantified. This is of conservation interest because management activities on prairie riparian corridors (e.g., timber harvest, impoundment and diversion of rivers and streams, livestock grazing) may have unintended consequences on habitats bats use for roosting and foraging, and may negatively impact bat populations. The Montana State Office of the BLM has designated five bat species as Sensitive: Pallid Bat (Antrozous pallidus), Townsend's Big-eared Bat (Corynorhinus townsendii), Spotted Bat (Euderma maculatum), Northern Myotis (Myotis septentrionalis), and Fringed Myotis (Myotis thysanodes). Each of these, along with Eastern Red Bat (Lasiurus borealis), is a state Species of Concern, and each has been documented in eastern Montana. The Montana Office of the BLM recognized the need for additional documentation of bats in eastern Montana riparian corridors to inform management activity, and initiated bat surveys across the eastern prairies in 2003 to address this need. We surveyed non-randomly chosen riparian sites for bats along the lower Missouri and Yellowstone rivers and tributaries (Tongue and Powder rivers in particular). This approach was targeted at identifying species richness at survey sites and may be useful for developing and implementing a state grid-based system for long-term monitoring.