Objective To summarize and analyze the monitoring Results of fleas in the plague natural foci of Meriones unguiculatus in Inner Mongolia, China from 2003 to 2012 and to provide reliable baseline data for analysis of the epidemic characteristics of enzootic plague in the natural foci and effective prevention and control of plague. Methods Surveillance was carried out in the 24 plague natural foci (banners or counties) of M. unguiculatus in Inner Mongolia, and stratified sampling was performed in different habitats. The opaque specimens of all ectoparasite fleas on captured rodents were classified under a low?magnification microscope. Fleas were collected from the burrow tracks of M. unguiculatus using sticks and then identified, and fleas were also collected from representative rodent holes. According to the criteria for determinating plague natural foci and plague epizootics (GB 16883-1997 and GB 16883-1997 Appendix B), the fleas were tested by culture of plague bacteria. The species, number, and infection of fleas in different years were recorded using Excel 2003 and analyzed by descriptive epidemiology. Results From 2003 to 2012, a total of 82 410 fleas, which belonged to 37 species (subspecies), 14 genera, 5 families, and 3 superfamilies, were collected in the plague natural foci of M. unguiculatus in Inner Mongolia. The annual number of flea species fluctuated between 26 and 32, and the annual number of fleas fluctuated between 6375 and 9891 (mean 8241). Plague bacteria were isolated from 930 fleas, which belonged to 14 species (subspecies). The annual number of species of plague bacteria isolated from fleas fluctuated between 0 and 9 (mean 3.3). The annual number of fleas from which plague bacteria were isolated fluctuated between 0 and 278 (mean 93). Stenoponia formozovi was found for the first time in the foci. Conclusion Because the ecological environment of plague natural foci has been affected by natural and social factors in recent years, the number, species, and infection of fleas show some new characteristics. We should strengthen the monitoring and control of the fleas as a vector in the transmission of plague.