【Objective】It is beneficial to explore effects of Sinorhizobium medicae (SM) and arbuscular mycorrhizal fungi (AMF) on alfalfa (Medicago sativa) growing in acid soils, to extrapolating the forage crop and promoting development of animal husbandry in Southwest China, so a micro field experiment was carried out.【Method】The experiment was designed to have 4 inoculation treatments, i.e. CK (blank control); SM (inoculation of SM); AMF (inoculation of AMF); and SM+AMF (inoculation of both SM and AMF) and carried out to study effects of the inoculations on nodulation, nutrient uptake, yield and quality of the alfalfa growing in an acid yellow soil, typical and representative of the studied region in Southwest China.【Result】Results show that the alfalfa in Treatment SM+AMF had more nodules, though smaller in size, a higher mycorrhizal infection rate, more rhizobacteria and mycorrhizal fungi infection sites on root surface, higher N fixation efficiency and a higher P absorption capacity than those in the other three treatments. Besides, the crop was also higher than the others in yield, contents of crude protein, crude fat and ashes, and accumulations of N, P, Ca and Mg in shoots, exhibiting significant synergy of the two inoculants. Compared with CK，both SM and AMF promoted plant growth, increased forage yield, and improved forage quality, but no significant difference between the two in these effects. In addition, the crop in Treatment SM was higher than that in CK in N content and accumulation of N, P and K in shoots, and higher than Treatment AMF in whole plant N accumulation. AMF stimulated the activities of nitrate reductase and roots, thus improving NO3-assimilation and nutrient uptake, which explains why the plant in Treatment AMF was higher than that in Treatment SM in P, K, Ca, and Mg content and accumulation in shoots. 【Conclusion】Both AMF and SM can promote uptake of N, P, and K by alfalfa and improve yield and quality of the forage to a varying extent. Therefore, inoculation of SM or AMF, particularly of both, is beneficial to cultivation of alfalfa in acid soils in Southwest China.