Melatonin promoted osteogenesis of bone marrow mesenchymal stem cells (BMMSCs) and inhibited RANKL expression which is involved in osteoclastogenesis. (a–c) alkaline phosphatase (ALP) levels were detected after osteogenic induction with melatonin for 7 days. (d) Mineralization nodes were observed by alizarin red staining after 21 days of osteogenic induction. (e, f) Protein (e) and gene (f) levels of Runx2, Osterix, and collagen I (Col‐I) were detected on Day 3 and Day 7 after melatonin treatment. (g) osteocalcin (OCN) expression was detected on Day 14 after melatonin treatment. (h, i) RANKL protein level (h) and the ratio of opg/rankl gene (i) were detected in bone marrow mesenchymal stem cells after melatonin treatment. Data are expressed as the mean ± SD and n = 5 in each group; *P < .05 significant differences between each indicated group. NS, not significant