FOXO3 and osteoporosis: The major novel findings of this study were exhibited: (1) TRIM33 expression in osteoblasts was positively correlated with the BMD of patients with osteoporosis; (2) TRIM33 raised the levels of FOXO3a protein and restrained its degradation; (3) TRIM33 restrained CBP‐mediated FOXO3a acetylation, thereby restraining FOXO3a ubiquitylation and degradation; (4) TRIM33 protected against the oxidative stress‐induced apoptosis of osteoblasts by raising FOXO3a expression; and (5) TRIM33 overexpression alleviated osteoporosis in OVX mice.