Abstract: Objective：To study the effects of activin receptor like kinase 2 (ALK2) on proliferation and differentiation of mouse pre-osteoblasts. Methods：The mouse pre-osteoblasts were cultured in vitro, silencing Alk2 gene by siRNA, detecting transfection by flow cytometry, using qRT-PCR to detect silence efficiency and the expression of genes related with osteogenesis. MTT method was used to detect cell proliferation and alizarin red staining was used to detect the ability of mineralization. Results：Mouse pre-osteoblasts were observed under inverted microscope. The cells were found to be irregular in shape, mostly triangular and polygonal, with more protuberances; flow cytometry and real-time RT-PCR showed that siRNA could reduce the expression of Alk2 in mouse pre-osteoblasts to 13%; MTT results showed that the number of cells increased after silencing Alk2 gene; the results of real-time RT-PCR showed that the expression of Runx2 decreased significantly(P<0.05) and the expression of Alp had downward trend after silencing Alk2 gene; alizarin red staining showed that the ability of mineralization decreased significantly after silencing Alk2 gene. Conclusions：ALK2 can inhibit the proliferation and promote the differentiation of mouse pre-osteoblasts.