Rumex crispus (curled dock), which is a perennial wild plant, has long been used as a laxative, astringent, and medicine to treat blood and skin diseases. We recently reported that the roots of R. crispus are an effective nutraceutical for bone. This study prepared ethanol extracts of the leaves and roots of R. crispus, and analyzed the major constituents using liquid chromatography and mass spectrometry. In addition, their effects on the proliferation and differentiation of human osteoblast-like MG-63 cells, such as cell viability, alkaline phosphatase (ALP) activity, collagen content, and mineralization, were compared. The chromatograms of the chemical constituents of the two extracts exhibited quite different profiles: quercetin and quercitrin were identified as major peaks in the leaf extract, whereas cinnamtannin B1 and procyanidin isomers were the major peaks for the root extract. Neither extract was cytotoxic at concentrations of < $25{mu}g/ml$. ALP activity and collagen synthesis-which are markers of the early stage of osteogenesis-in MG-63 cells were significantly increased upon the addition of the root extract compared with the addition of the leaf extract. In contrast, the leaf extract had a more stimulatory effect on mineralization-which is marker of the late stage of osteogenesis-in MG-63 cells than did the root extract. In conclusion, extracts of both leaves and roots of R. crispus stimulated the bone-forming activity of osteoblasts; in particular, the root extract was more effective in the early stage of osteoblast differentiation, while the leaf extract was more effective in the late stage. This difference in anabolic activity may be due to differences in the constituents of the leaves and roots. The leaves and roots of R. crispus appear to complement each other as stimulators of bone formation.