Curcumin, an active component of the rhizomes of Curcumin longa L., possess broad anti‐inflammation and anti‐cancer activities. Curcumin was previously reported to be capable of protecting ovariectomized rats against osteoporosis. However, the effect of curcumin on glucocorticoid‐induced osteoporosis (GIO) is not clear yet. The present study investigated the effects of curcumin on dexamethasone (Dex)‐induced osteoporosis in vivo and Dex‐induced osteoblast apoptosis in vivo and in vitro. The GIO rat model was induced by subcutaneous injection of Dex for 60 days and verified to be successful as evidence by the significantly decreased bone mineral density (BMD) using dual X‐ray absorptiometry. Subsequently, curcumin administration (100 mg/kg) for 60 days obviously increased BMD and bone‐alkaline phosphatase, decreased carboxy‐terminal collagen cross links, enhanced bone mechanical strength, and improved trabecular microstructure, thereby alleviating Dex‐induced osteoporosis. Mechanically, curcumin remarkably reserved Dex‐induced femoral osteoblast apoptosis in vivo. In cultured primary osteoblasts, pretreatment with curcumin concentration‐dependently decreased the number of Dex‐induced apoptotic osteoblasts by down‐regulating the ratio of Bax/Bcl‐2 as well as the levels of cleaved caspase‐3 and cleaved PARP. Moreover, curcumin pretreatment activated extracellular signal regulated kinase (ERK) signaling in Dex‐induced osteoblasts by up‐regulating the expression level of p‐ERK1/2. Taken together, our study demonstrated that curcumin could ameliorate GIO by protecting osteoblasts from apoptosis, which was possibly related to the activation of ERK pathway. The results suggest that curcumin may be a promising drug for prevention and treatment of GIO. This article is protected by copyright. All rights reserved.