Polygonum multiflorum Thunb. is a traditional Chinese medicinal herb that has been widely used to treat age-associated diseases. Tetrahydroxystilbene glucoside (TSG), also known as 2,3,5,4-tetrahydroxystilbene-2-O-β-D-glucoside, is a major component of this herb. The present study was designed to investigate the osteogenic differentiation promoting activity of TSG in rat mesenchymal stem cells (MSCs) and in zebrafish. Preliminary experiments using MTT assay and ALP methods indicate that the high potential activity for promoting osteogenic differentiation was observed when 50% ethanol eluate was used. Further isolation and purification of TSG from the 50% ethanol eluate was performed by bioassay-guided fractionation, and its structure was confirmed using nuclear magnetic resonance and mass spectrometry analyses. In addition, the relative content of TSG with the highest potential activity in the promotion of osteogenic differentiation was identified as 14.34% by reversed-phase high performance liquid chromatography. Subsequently, the osteogenic differentiation promoting abilities of TSG in MSCs were examined. The results demonstrated that TSG promoted the alkaline phosphatase activity at concentrations of 1.56-25 µg/ml, while it increased the content of osteocalcin 7 days after treatment with 6.25-25 µg/ml in MSCs. Furthermore, experiments in zebrafish indicated that different concentrations of TSG (3.12-12.5 µg/ml) protected against further bone loss induced by 10 µmol/l dexamethasone (Dex), simulating an osteoporosis (OP) model. TSG treatment (12.5 µg/ml) in Dex-induced zebrafish significantly increased the area of nodules by 50.14% compared with the untreated model group. In conclusion, TSG, as a major component of P. multiflorum Thunb. exhibited an osteogenic promoting activity in MSCs and in zebrafish. The results provided scientific evidence to support the potential use of TSG for protecting the bone in degenerative diseases, such as OP.