BACKGROUND:Several studies have shown that plant saponins promoted osteoblast differentiation and improved osteoporosis. In current study, sea cucumber saponins (SCS) with a purity of 80% was extracted from Filipino sea cucumber, with a similar structure to plant saponins. OBJECTIVE:This study aims to investigate the effects of SCS on bone formation in vitro and ex vivo. RESULTS:SCS significantly promoted osteogenic differentiation and mineralization of MC3T3-E1 cells, as well as new osteoid formation in neonatal mouse calvarias ex vivo. qRT-PCR results indicated that SCS markedly down-regulated the expression of C/EBPα* and PPARγ at the levels of transcription, which demonstrate that SCS inhibit the trans-differentiation of MC3T3-E1 cells to an adipocytic phenotype. What is more, further studies revealed that SCS increased the expression levels of Runx2 and OSX. The mechanism revealed that SCS induced the expression of BMP2 and p-Smad1/5, which indicated that SCS facilitated osteogenesis via activating the BMP2/Smads signaling pathway. CONCLUSION:SCS promoted osteogenic differentiation of pre-osteoblasts by activating BMP2/Smads molecular pathway, providing theoretical basis for the development of sea cucumber saponins for the treatment to bone loss diseases such as osteoporosis.