Abstract: Pot experiments were conducted to evaluate the growth and drought resistance of alfalfa (Medicago sativa) seedlings colonized by Piriformospora indica fungus. The experiment comprised a 2×2 factorial combination of inoculation (inoculated, I, or un-inoculated, NI) and drought (droughted, D or not, ND) treatments, giving 4 combinations: I-D, I-ND, NI-D (reference), and NI-ND. For the inoculated plants, 40 mL of inoculant with P. indica mycelium was applied, and for control plants, 40 mL of sterile water was added. Soil water content was 75%-80% of field capacity for the normal irrigation treatment and 15%-20% for the drought treatments. Fresh shoot and root weights, root length, dry shoot and root weights, chlorophyll (SPAD), relative water content (RWC), antioxidase enzyme activity, , methane dicarboxylic aldehyde (MDA) and osmolytes were determined for all treatments. The fungus strongly colonized the roots of alfalfa, infecting 87.4% of seedlings. When the colonized plants were exposed to drought stress, the fresh shoot weight, dry shoot weight, chlorophyll, relative water content and the number of leaves per plant were promoted significantly by 63.4%, 69.2%, 12.5%, 17.1% and 5.7, respectively. In addition the fresh root weight, dry root weight, length of taproot and number of lateral roots were improved significantly by 33.3%, 57.1%, 5.1 cm and 5 roots, respectively, compared to the reference plants (NI-D). Furthermore, the activities of super-oxide, peroxidases, catalases, and the levels of proline and of soluble sugar in the leaves increased by 1.71, 1.27, 1.22, 1.49 and 1.48 times, respectively, and the contents of and MDA decreased significantly. In summary, P. indica fungus enhanced the growth and drought tolerance of alfalfa in the seeding stage by stimulating the activity of antioxidant enzymes and the content of osmolytes, while under normal irrigation, the fungus had no significant effect on the growth of alfalfa.