Determinig habitat suitability and abundance estimation is essential for conservation and management of wildlife resources. Historically Persian wild ass, Equus hemiounus onager , were widespread in arid and semi arid steppes of central Iran, but today only two natural populations have remained. Onager is endemic to Iran. This suecies is listed as critically endangered (CR) in the Red List of the International Union for Conservation of Nature (IUCN). The main factors contributed to the population decline of the suecies include poaching, competition with domestic animals, protection problems, drough and geographical isolation and loss of genetic variability. Accurate knowledeg about population size and habitat assocaiations of this threatened species is essential for its successful consevation. We studied population density and habitat associations of Persian wild ass in Touran Protected Area . Ecological Niche Factor Analysis (ENFA) was applied for modeling and the species habitats. Frequency of water sources, frequency of rivers, geomorphologic types, geologic types, vegetation types, average annual minimum temperature, average annual precipitation, slope, aspect, frequency of plains, altitude, distance to livestock corrals, distance to roads and distance to villages were used as environmental variables in the analyses. The presence of wild asses in the area was documented by GPS points from October 2009 to September 2010 by patrolling in the area. Frequency of water sources, average annual precipitation, geomorphologic types, distance to livestock corrals and plant types were the most important factors determining habitat suitability of Persian wild ass. Suitable habitats were located in areas with averaged minimum temperatures of 10 to 12 C° and areas close to the hills and upper terrace where plant species such as Artemisia , Zygophyllum and Pteropyrum are dominant and are not far too far from livestock corrals. Habitat suitability maps were produced using Distance geometric mean algorithm, distance harmonic mean algorithm and Minimum distance algorithm with acceptable accuracy. The model entral parts of the area , where is recognized as the most suitable habitat for onagers (included Harb Plain, Probal, Majerad, Shah Zinab, Parie Plain, Chah Madan, Kal Mora, Seghadir and Dokali) was estimated. The area (c. 1489 km 2 ) were traversed on distance sampling line transects along the Keywords: Persian wild ass, Habitat suitability, Ecological Niche Factor Analysis,.Estimate population, Line transect
