Evaluating plant diversity in various ecological conditions is required to develop appropriate conservation plans and enhance natural ecosystem conditions. This study aimed to identify the most influential factors on variations of plant diversity in Valuyeh of Kiyasar summer rangeland in Mazandaran province. Random-systematic sampling approach was used to collect vegetation and soil data along with LFA indices from the sites located 1600 to 2200 meters from sea level with north and south aspect. The plant diversity was determined using entropy Shanon, Sympson, Jini and Sympson indices and plant richness were determined by counting plant species. Multivariate analysis was used to identify the major ecological groups and explore the effects of topographical features and LFA indices on plant diversity in the study area. According to the results, the elevation from sea level and soil stability parameters in the sites located in north aspect, and elevation from sea level, soil infiltration and soil texture in the sites located in south aspect were identified as the most influential factors on plant diversity in this region. Secale montanium-Festuca ovina ecological group with 116 species and Lolium perene- Medicago sativa ecological groups with 119 species had the highest species richness in north and south aspect sites, respectively.