Abstract: The deficiency of available phosphorous (P) in most of the soils in China restricts increases of crop production. There have been many studies on the responses and adaptation to phosphorus deficiency of different plant species in the literature, but there is little information on the effect of phosphorus deficiency on physiological properties of pasture plants, especially native legumes of temperate grassland. In this study, the effect of phosphorus deficiency was studied on two ecotypes (Ximeng and Humeng) of Medicago falcata, which is an important legume in temperate grasslands of northern China and which has good tolerance to cold, drought and infertile soils. The two ecotypes differed in their responses to phosphorus deficiency. There were no significant differences in biomass, area, length and volume of root system, phosphorus content in shoots, or net photosynthetic rate between the two ecotypes under phosphorus-sufficient (500 μmol/L H₂PO₄^-) conditions. However, there were greater reductions in biomass, area, length and volume of root system, shoot phosphorus content and net photosynthesis rate in Humeng than Ximeng ecotypes after low phosphorus treatment (5 μmol/L H₂PO₄^-). Further, there was more exudation of citrate from Ximeng than Humeng ecotypes under phosphorus-deficient conditions. Taken together, the tolerance to phosphorus deficiency of Ximeng is greater than that of Humeng.