Rangelands are natural ecosystems containing great genetic resources and plant species diversity having profound effects on stability of the rangelands. A most obvious and destructive biotic factor on this vegetation is overgrazing by animals. Therefore a study was carried out in two different grazed and ungrazed sites of rangeland vegetation in kohneh lashak Kojour, 65 km to South of Nowshahr, Mazandaran province to examine the effects of animal grazing on the rangeland conditions. Minimal area of 1 square meter was obtained by using nested quadrat method. Based on cumulative mean of dominant species, 20 quadrats were located in each site on two 100 m transects according to random-systematic sampling strategy. Species composition and their abundance were recorded. The result of field investigation was collection and identification of the total 102 plant species from which 99 and 58 species were recorded in the ungrazed and grazed sites, respectively. The collected abundance data were subjected to analyses by specific diversity packages to characterize and obtain numerical and parametric indices of species diversity. The results of numerical indices showed a higher species richness, evenness and species diversity indices in ungrazed than in the grazed site. Statistical t-test was significant in 0.05 significance level based on Shannon Index. Diversity comparing in the two sites by using rank-abundance plot as well as diversity ordering of Hill, Renyi and Patil and Taillie showed a higher species diversity in the ungrazed site that can explain the wellbeing of the environmental condition of this site.