Abstract: The specific leaf weight values(SLW-fresh weight of leaves/area of leaves)of 7 common tree species grown in loess plateau area, i.e., Robinia pseudoacacia, Amorpha fruticosa, Caragana korshinskii, Populus davidiana, Hippophae rhamnoides, Sophora japonica and Rosa hugonis were calculated and the relationship between the SLWvalue and photosynthetic capacity of the leaves was studied.It was showed by the results that there was significant correlation between the leaf area and the fresh leaf weight for these 7 tree species, and the SLWshowed significant variation alongwith the seasons.These variations were closely related with the growth rhythm and the differences in nutrients utilization and storage patterns for different tree species.In growing season, the order of average SLW value was Hippophae rhamnoides >Caragana korshinskii >Robinia pseudoacacia > Sophora japonica >Amorpha fruticosa >Populus davidiana >Rosa hugonis.The SLWdiffered among these 7 tree species and the value of SLW for the same tree species also varied with the time, reflecting the differences in leaf development process for different tree species and in different seasons.It was found out that the SLW values of Robinia pseudoacacia, Caragana korshinskii, Populus davidiana and Amorpha fruticosa were significantly positively related to the photosynthetic capacity of the leaves, i.e., the photosynthetic capacity increased along with the increment of SLW value, the regression relationship for Robinia pseudoacacia could be expressed as exponential function, and for Populus davidiana was a linear function.The regression formulae between SLWand photosynthetic capacity for Caragana korshinskii and Amorpha fruticosa were quadratic functions.Under the critical point of SLW, the photosynthetic capacity increased as the SLW increased, but it decreased when the SLW was over the critical point.There was no significant relationship between the SLW and photosynthetic capacity for Rosa hugonis, Sophora japonica and Hippophae rhamnoides.