Circulating microRNAs (miRNAs) play important roles in regulating gene expression and have been reported to be involved in various metabolic diseases, including osteoporosis. Although the transcriptional regulation of osteoblast differentiation has been well characterized, the role of circulating miRNAs in this process is poorly understood. Here we discovered that the level of circulating miR‐19b was significantly lower in osteoporotic patients with vertebral compression fractures than that of healthy controls. The expression level of miR‐19b was increased during osteoblastic differentiation of human mesenchymal stem cells (hMSCs) and MC3T3‐E1 cells, and transfection with synthetic miR‐19b could promote osteoblastic differentiation of hMSCs and MC3T3‐E1 cells. PTEN (phosphatase and tensin homolog deleted from chromosome 10) was found to be directly repressed by miR‐19b, with a concomitant increase in Runx2 expression and increased phosphorylation of AKT (protein kinase B, PKB). The expression level of circulating miR‐19b in aged ovariectomized mice was significantly lower than in young mice. Moreover, the osteoporotic bone phenotype in aged ovariectomized mice was alleviated by the injection of chemically modified miR‐19b (agomiR‐19b). Taken together, our results show that circulating miR‐19b plays an important role in enhancing osteoblastogenesis, possibly through regulation of the PTEN/pAKT/Runx2 pathway, and may be a useful therapeutic target in bone loss disorders, such as osteoporosis.