Chemical investigation of the stems and leaves of Rhus Sylvestris afforded a new megastigmane glycoside named rhusonoside A ( 1), along with four other known compounds: dihydroquercetin ( 2), astragalin ( 3), hyperin ( 4), and kaempferol-3- O-rutinoside ( 5). Their structures were determined by a combination of spectroscopic analysis and application of the modified Mosher's method. The effect of compounds 1 - 5 on the function of osteoblastic MC3T3-E1 cells was examined by determining cell viability, alkaline phosphatase (ALP) activity, collagen synthesis, and mineralization. Rhusonoside A ( 1) significantly increased the function of osteoblastic MC3T3-E1 cells. Cell viability, ALP activity, and collagen synthesis were increased dose dependently, up to 155.39 %, 171.27 %, and 134.25 %, respectively, of the basal value at 10 muM ( P < 0.05). In addition, 0.1 muM of compound 1 significantly increased mineralization of MC3T3-E1 cells to 142.78 % ( P < 0.05) of the basal value.