miRNAs are endogenously expressed 18- to 25-nucleotide RNAs that regulate gene expression through translational repression by binding to a target mRNA. Recently, it has been indicated that miRNAs are closely related to osteogenesis. Our previous data suggested that miR-30 family members might be important regulators during the biomineralization process. However, whether and how they modulate osteogenic differentiation have not been explored. In this study, we demonstrated that miR-30 family members negatively regulate BMP-2-induced osteoblast differentiation by targeting Smad1 and Runx2. Evidentially, overexpression of miR-30 family members led to a decrease of alkaline phosphatase activity, whereas knockdown of them increased the activity. Then bioinformatic analysis identified potential target sites of the miR-30 family located in the 3' untranslated regions of Smad1 and Runx2. Western blot analysis and quantitative RT-PCR assays demonstrated that miR-30 family members inhibit Smad1 gene expression on the basis of repressing its translation. Furthermore, dual-luciferase reporter assays confirmed that Smad1 is a direct target of miR-30 family members. Rescue experiments that overexpress Smad1 and Runx2 significantly eliminated the inhibitory effect of miR-30 on osteogenic differentiation and provided strong evidence that miR-30 mediates the inhibition of osteogenesis by targeting Smad1 and Runx2. Also, the inhibitory effects of the miR-30 family were validated in mouse bone marrow mesenchymal stem cells. Therefore, our study uncovered that miR-30 family members are key negative regulators of BMP-2-mediated osteogenic differentiation.