MiR-133b is considered to be lowly expressed in osteoporosis patients. This study aimed to probe the role and in-depth mechanism of miR-133b in modulating osteoblast biological behavior and differentiation. The differential expressions of miR-133b and GNB4 in patients with osteoporosis and healthy control were analyzed based on the GEO database. Osteoblastic differentiation of hFOB 1.19 cells was induced in the culture medium containing 10 mM β-glycerophosphate, 50 nm dexamethasone, and 100 μg/ml ascorbic acid. The level of GNB4 was detected using quantitative real-time PCR (qRT-PCR) and Western blot. Cell viability and apoptosis were measured by Cell Counting Kit-8 (CCK-8) and flow cytometry assays, respectively. Western blot was also utilized to measure the levels of osteoblast-related proteins, including ALP, Runx2, Osterix, and OPN. GNB4 was identified and confirmed as a downstream target gene of miR-133b. The expression of miR-133b was declined while the expression of GNB4 was increased in osteoporosis patients. Importantly, up-regulation of miR-133b caused the increase of cell viability and the decrease of apoptosis, which could be blocked by overexpression of GNB4. Also, up-regulation of miR-133b promoted osteoblasts differentiation, as shown by the increase in the expression of ALP, Runx2, Osterix, and OPN. Similarly, this promoting impact resulted from miR-133b overexpression can be reversed via up-regulation of GNB4. These findings revealed that miR-133b can promote the viability and differentiation of osteoblasts by targeting GNB4, hoping to lay a feasible theoretical foundation for the clinical treatment of osteoporosis.