As the soil affect plant species, plant species also specifically affect the soil. Different variations of chemical, biological and physical create by the activity of plant roots in the area ‌surrounding the plant roots (rhizosphere). Astragalus cyclophyllon and Hedysarum criniferum are the perennial, native and valuable forage species of Iran rangelands. The present study was conducted to investigate the effects of A. cyclophyllon and H. criniferum as the nitrogen fixing plants on some properties of the soil in the Watershed Research Station located in the chadegan. To achieve the goal, samples of the understory soil of A. cyclophyllon, H. criniferum, Bromus tomentellus as a control plant (non-legume and non- nitrogen fixing plants) and the control soil (where no plant is not present) at two depths 0-30 and 30-60 cm with three replications were analyzed based on completely randomized design. The properties of the soil, including CaCO3, EC, pH, organic carbon, inorganic nitrogen, total nitrogen percent in soil, The ratio of carbon to nitrogen and soil texture were measured. Likewise, analysis of the criterion plant was studied to determine the efficiency of these lant on amount of total nitrogen and production of understory plant at laboratory scale. Results showed that the amount of inorganic nitrogen, total nitrogen content and organic carbo as well as the criterion plant’s total nitrogen content and plant production at 0-30 cm were significantly different from other treatments (p 0/05) and were decreased with the increased depth. Generally, the effect of vegetation was significant in the majority of studied parameters and there were a significant difference among the studied species, control soil and control vegetation treatments which reflects the positive effect of the nitrogen fixing plants on properties of the soil compared to control soil. Keywords : Astragalus cyclophyllon , Hedysarum criniferum , organic carbon, nitrogen content, criterion plant.