The number of Przewalski's horses(Equus przewalskii) released increased from 84 in 2011 to 96 in 2012 in the Mt. Kalamaili Ungulate Nature Reserve. We characterized the home ranges of released Przewalski's horses and studied the factors affecting the ranges. The home ranges were calculated using the minimum convex polygon(MCP) method. We used a nested ANOVA to determine whether there were differences between home ranges, and regions of overlap between two home ranges of wild horses among seasons and years. We also used family size as a covariate to test the impact of family size on home ranges using ANCOVA. We found the following results:(1) the home ranges of released Przewalski's horses increased in area from(20±2) km²(mean±SE) in 2011 to(30±2) km² in 2012. The home ranges of families with the same head stallion did not change significantly between 2011 and 2012(P < 0.05).(2) ANOVA indicated that home ranges differed significantly among families. The home ranges of horse families were significantly different, were larger in the spring than in the autumn, and were the smallest in the summer.(3) The area of home range overlap between pairs of wild horses was not correlated with family size(r=0.256, P=0.580) in 2011. However, the area of overlap between pairs of wild horses was correlated with family size in 2012(F=4.521, d f=8, P < 0.001). Home range overlap and family size were significantly positively correlated(r=0.706, P=0.033).(4) Regions of home range overlap between wild horses were significantly different among seasons(F=5.695, d f=8, P < 0.001). The regions of overlap in seasonal home ranges for families 5, 7, and 8 were significantly larger(P < 0.05) than those for families 3, 6, and 9(P < 0.05).(5) The main biological factors that affected the home range of wild horses were herb coverage and shrub coverage, and the non-biological factors were mainly temperature, humidity, wind, the shortest distance to a water source, and distance to the nearest human settlement. Temperature and shrub cover were two major factors that influenced the home ranges of reintroduced Przewalski's horses, and both factors were significantly correlated with the home range areas of wild horses(P < 0.01). Domestic research on wildlife home ranges has been interdisciplinary in nature, and previous investigations have led to the progressive development of large-scale multidisciplinary studies. Furthermore, research tools have advanced from records of single manual observations to computer-based methods, including 3S technology(i.e., RS, GPS, and GIS). Estimates of home range sizes can help researchers determine wildlife habitat preferences, and 3S technology is widely used to protect wildlife. Finally the methods for calculating home ranges of wild animals are becoming more diverse. Przewalski's horses are a flagship species for biodiversity in the Junggar Basin. Their reintroduction has attracted widespread interest at home and abroad. At the end of 2012, the number of reintroduced Przewalski's horses increased to 96(from 84 in the previous year). Therefore, it is necessary to study changes in the home range of wild Przewalski's horses in detail in order to provide scientific guidance for the protection of wildlife in protected areas as well as in the Mt. Kalamaili Ungulate Nature Reserve desert region of Xinjiang, China.