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In order to evaluate the grazing capacity as well as to implement an integrated management of rangelands, it is necessary to be aware of forage quality. The most important factor influencing forage quality is the plant growth stage, which presents the most suitable time for animal grazing. In this research, samples were taken (using randomized- systematic design) from three grasses and from two forbs, namely Agropyron tauri, Dactylis glomerata, Bromus tomentellus, Ferula ovina, and Coronilla varia. Samples were collected at three phenological stages of vegetative growth, full flowering, and seed ripening from summer ranges in central Alborz (Vardavard and Gachsar). Plant samples were dried, milled, and chemically analyzed for important qualitative factors such as: DM, NDF, ADF, CP, ME, DDM, DMI, WSC, RFV. Except for DM, there were significant differences (p<0.01) observed among different species as well as among different phenological stages. Also, interaction effects of plant species and growth stages were observed to be significant for these factors. Almost in all species, the amount of CP, DDM and ME decreased with progressing growth stages, while ADF and NDF contents increased. In general, crown vetch (Coronilla varia) had the highest forage quality based on the assessed factors (RFV=257.9) and in this respect, Agropyron tauri possessed the lowest (RFV=92.1). F.ovina, D.glomerata and B.tomentellus respectively had a greater nutritive value after C.varia. Vegetative growth (first phenological stage), considering all nutritive factors (except WSC), benefited from higher values in comparison with the other stages. Considering low energy differences between first and second phenological stages and also because of higher production, and pasture availability, the second stage(flowering)was determined as the most suitable period for animal grazing (in the framework of grazing systems).