With the acceleration of aging population in the world, the incidence of age-related bone loss has shown an obvious rising trend. It is of great significance to find effective approaches to relieve senile osteoporosis. Nobiletin is one of the most abundant flavonoids in citrus genus with many important biological properties. Herein, 20-month naturally aging mice were used as senile osteoporosis model and were treated with nobiletin by consecutive intraperitoneal injection for 15 days. Micro-CT results showed that nobiletin significantly improved the bone microstructure featured by increased bone volume fraction and decreased trabecular separation. HE staining results indicated that nobiletin increased the number of osteoblasts of trabecular bone surface. Serum osteocalcin (gene Bglap) level was also found to be significantly increased in mice by nobiletin treatment. We then tested the effect of nobiletin in mouse pre-osteoblast (MC3T3-E1 cells) model and found that nobiletin significantly up-regulated Mki67 expression, increased Bglap expression and alkaline phosphatase enzyme activity, and markedly enhanced the alizarin red S staining, suggesting that nobiletin can promote osteoblast proliferation, differentiation and mineralization. Further study of the underlying mechanism showed that nobiletin increased the retinoic acid receptor-related orphan receptor α (RORα, gene Rora), down-regulated sclerostin (SOST, gene Sost) and up-regulated osteocalcin, while knocking down of Rora significantly compromised the regulation of nobiletin on Sost and Bglap, indicating that the improving effect of nobiletin on age-related bone loss depends on RORα. To our knowledge this is the first report that nobiletin shows improvement effect on bone loss in naturally aging mice and the first report that nobiletin down-regulates Sost through Rora. These results provide a new mechanism of nobiletin in age-related bone loss and a new potential strategy to improve the senile osteoporosis.