Bone injury following radiotherapy has been confirmed by epidemiological and animal studies. However, the underlying mechanism remains to be elucidated and no preventive or curative solution has been identified for this bone loss. The present study aimed to investigate the irradiation‑altered osteogenesis and adipogenesis of bone marrow mesenchymal stem cells (BMSCs). BMSCs were derived and exposed to γ‑irradiation at doses of 0, 0.25, 0.5, 1, 2, 5 and 10 Gy. Cell viability was assessed using a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5 diphenyl tetrazolium bromide assay, and clonal expansion in vitro was detected by colony forming unit assessment. The osteogenic differentiation ability was demonstrated by alkaline phosphatase (ALP) activity, ALP staining and mineralization alizarin red staining, and the adipogenic differentiation ability was determined using Oil O red staining. The osteogenesis‑associated genes, RUNX2, ALP, osteocalcin (OCN) and adipogenesis‑associated genes, PPAR‑γ and C/EBPα, were detected using reverse transcription‑quantitative polymerase chain reaction analyses. The protein expression levels of RUNX2, ALP and PPAR‑γ were detected using western blotting. Compared with the control, significant decreases in the proliferation, ALP activity and mineralization ability of the BMSCs were observed in the γ‑irradiation group, with a high level of correlation with the exposure dose. However, no significant changes were observed in the area of Oil red O positive staining. The mRNA levels of RUNX2, ALP and OCN were decreased (P<0.05), however, no significant changes were observed in the levels of C/EBPα and PPAR‑γ. The protein expression levels of RUNX2 and ALP were decreased in the irradiated BMSCs, however, no significant difference was observed in the protein expression of PPAR‑γ. Irradiation inhibited the osteogenic and adipogenic ability of the BMSCs, and the osteogenic differentiation was decreased. The results of the present study provided evidence to assist in further elucidating radiotherapy‑associated side effects on the skeleton.