To evaluate the effects of biofertilizers on some physiological growth indices of a soybean cultivar (M9) under water stress condition, a study was carried out in a split plot randomized complete block design in three replications at research station of Bu Ali Sina University, Hamedan, Iran in 2012. The main plots consisted of three levels of irrigation after 50, 100 and 150 mm evaporation from a Class-A evaporation pan and subplots consisted of four biological fertilizer treatments (seed inoculation with Bradyrhizobium japonicum, application of arbuscular mycorrhizae, both biofertilizers and no biofertilizer). The results showed that with increase in the water stress level all measured growth indices including maximum crop growth rate, maximum total dry matter and total dry matter duration were decreased. The three latter growth indices were decreased by 63, 50.8 and 47.6 percent, respectively, in severe water stress compared to the non stress condition. Application of biofertilizers in general and mycorrhizae in particular led to decreases in the measured growth indices in the absence of water stress. But at the presence of severe water stress (i. e. irrigation after 150 mm evaporation) simultaneous application of both biofertilizers led to significant increases in a majority of the growth indices including maximum crop growth rate, maximum leaf area index and total dry matter duration (by 50, 28.6 and 45.8 percent, respectively) compared to no-biofertilizers application.