In this research the effects of mycorrhizal symbiosis and irrigation intervals on growth indices and grain yield of two sorghum cultivars was studied. Field experiment was laid out as a split plot factorial based on randomized complete block design with three replications. Irrigation intervals as main factor in three levels (7, 14 and 21days) and factorial combination of two sorghum cultivars (Kimia and Sepideh) with three levels of seed inoculation (non inoculation, inoculation with Glomus intraradices and inoculation with Glomus mossea) were considered as sub-plots. Results showed that maximum values of leaf area index (4.21), crop growth rate (50.8 g m-2 day-1) and total dry matter (1852.5 g m-2) without significance difference with 14 days irrigation interval, were achievedat 7 days irrigation interval. In comparison with non inoculation treatment, Glomus mossea increased leaf area index, crop growth rate and total dry matter up to 17.4, 11 and 8.6 percent, respectively. Also, growth indices of Kimia cultivar were superior to Sepideh cultivar. Without significant difference with plants inoculated with Glomus mossea and 14 days irrigation interval, maximum grain yield was achieved at plants inoculated with Glomus mossea and 7 days irrigation interval which in comparison with treatment of non-inoculation and 21days irrigation interval, increased grain yield of sorghum by 56.47 percent. In general, results indicated that mycorrhizal fungi especially Glomus mossea improved plant growth indices and yield of sorghum under deficit irrigation (14 days irrigation interval).