Long-term drought effect is one of the main factors of global climate change, which have consequences for soil carbon cycle and function of soil ecosystems and plant efficiency. We hypothesized that sensitive and drought tolerate genotypes could differ in their rhizosphere responses to drought condition. We examined carbon and nitrogen microbial biomass, enzyme activity of ?-glucosaminidase, organic carbon, and nitrogen in the rhizosphere of sensitive and drought tolerant genotypes of Bromus inermis , Dactylis glomerata and festuca arundinacea species under 5 years drought treatments at Lavark Farm of Isfahan University of Technology. Effects of drought treatments, species and genotypes on soil microbial carbon and nitrogen, ?-glucosaminidase and soil organic carbon and nitrogen were analyzed using SAS 9.4 software. Across species and genotypes, we found that Dactylis species and sensitive genotypes experienced the most rhizosphere MBC decline. In addition, there was a significant decrease in MBN in rhizosphere of Fescue and Bromus under drought. The lowest MBC and MBN was observed in drought-sensitive genotype. Organic carbon, inorganic nitrogen, total nitrogen and carbon to nitrogen ratios were not significantly affected by drought stress. However, inorganic nitrogen was significantly higher in the control soil than in the rhizosphere soil of the three species, but the organic carbon content in the control soil was lower than in the rhizosphere soil of the three species. The results showed that the activity of ?-glucosaminidase did not respond to any of the moisture treatments, species and genotypes. Principle Component Analysis showed that Bromus inermis -tolerant-13 is the best genotypes for C and N accumulation in soil pools under drought and without drought stress. The present study showed that long-time drought stress and adaptation to grasses and microbial populations cause changes in carbon and nitrogen biomass of soil, which may have important consequences for ecosystem services such as productivity, biodiversity and soil quality. Key words Microbial biomass carbon, Microbial biomass Nitrogen, ?-glucosaminidase enzyme, Drought, Grasses, Drought tolerate genotype, Drought sensitive genotype.