The availability of wild prey is a critical predictor of carnivore density. However, few conservation programmes have focused on the estimation and monitoring of wild ungulate populations and their trends, especially in the remote mountains of Central Asia. We conducted double-observer surveys to estimate the populations of ibex Capra sibirica and argali Ovis ammon in the mountainous regions of Tost Local Protected Area, South Gobi province, Mongolia, which is being considered for designation as a Nature Reserve. We also conducted demographic surveys of the more abundant ibex to examine their sex-ratio and the survival of young during 2012–2013. The estimated ibex population remained stable in 2012 and 2013 and the estimated argali population increased from 108 in 2012 to 230 in 2013. The biomass of wild ungulates was c. 6% that of livestock. Mortality in young ibex appeared to increase after weaning, at the age of 12 months. We estimated the population of wild ungulates was sufficient to support 14–18 adult snow leopards Panthera uncia. The adult snow leopard population in our study area during 2012–2013, estimated independently using camera-trap-based mark–recapture methods, was 12–14. Based on our results we identify the Tost Local Protected Area as an important habitat for the conservation of these ungulates and their predator, the Endangered snow leopard, and recommend elevation of its status to a Nature Reserve.