Isopsoralen (ISO) inhibits bone-derived marrow mesenchymal stem cell (BMSC) differentiation into adipocytes in vitro. ISO (5, 10 or 20 µM) was added to primary mouse BMSCs following adipogenic differentiation. (A) Peroxisome proliferator-activated receptor γ (PPARγ) immunocytochemistry and (B) CCAAT/enhancer binding protein β (C/EBPβ) immunofluorescence assays were performed to examine the expression of adipocyte-specific proteins following treatment with ISO. (A) ISO increased PPARγ expression (brown) in BMSCs in a dose-dependent manner, with the most pronounced effect at 20 µM (C). (B) ISO dose-dependently enhanced C/EBPβ activity (green) in BMSCs, particularly at 20 µM (D). *P<0.05, **P<0.01 and ***P<0.001 compared to the group without ISO (Con, control). Columns represent the means ± SD from 9 wells/group (C and D).