AbstractThe global population of saiga Saiga tatarica, categorized as Critically Endangered on the IUCN Red List, declined by > 95% at the end of the 20th century, resulting in several conservation initiatives to protect the species. Previously used methods to monitor population trends were inadequate to assess numbers of saiga properly. We report findings from the first survey for Mongolian saiga S. tatarica mongolica to utilize statistically rigorous methodology, using line transect distance sampling in 2006 and 2007 to obtain population estimates in and around the Sharga Nature Reserve, the southern part of the species' current range. We estimate a density of 0.54 and 0.78 saiga km^-2 in 2006 and 2007, respectively. Our best models suggest that 4,938 (95% confidence interval, CI = 2,762–8,828) saiga occupied the 4,524-km² study area in 2006 and 7,221 (95% CI = 4,380–11,903) occupied the 4,678-km² study area in 2007. Although these estimates, with their large confidence intervals, preclude an assessment of the impacts of conservation initiatives on population trends, they suggest that the Mongolian saiga population is larger than previous reports based on minimum counts, and adequate to support in situ population recovery. Modifications to the survey protocol hold promise for improving the precision of future estimates. Distance sampling may be a useful, scientifically defensible method for monitoring saiga population trends and assessing the effectiveness of conservation efforts to stabilize and recover populations.