Determination of the factors affecting on species distribution and diversity is the most important factor in ecosystems management. The study on plant species diversity in different elevations of Nova Mountain located in 10 km Dalahou was aimed. For this purpose, 240 plots were selected based on a random-systematic design according with minimal area method. All the plots were divided into three altitudinal classes. ANOVA analysis used to study of altitudinal class differences with species richness and species diversity indices. In total, 177 species belong to 128 genera and 37 families were recognized. Therophytes with 69 species (38.98%) were the most frequent life forms. The results showed that the highest number of species is related to lower elevations class (1600 to 1900 m a.s.l.). Irano-Turanian species had the highest number in the studied area. Analysis of variances for biodiversity indices in different altitudinal classes showed the indices of species richness and species diversity have significant differences at the 0.05 and 0.01 levels, respectively. In total, results showed the elevation has significant effect on species richness and diversity in which, the higher elevations class has lower species diversity.