Objective To study the age-related changes of rat bone histomorphometry and its correlation to other parameters of bone metabolism. Methods Ten female SD rats at the age of 3 months old,9 months old and 15 months old were labeled with tetracycline(30 mg/kg) via abdomen on fourteen and four days before executing. Histomorphometry were performed on L4 and right tibiae. Physical density of left femur and L2 were measured. Anti-compression property of L3 was assayed. Serum levels of calcium and phosphorus and 1,25(OH)_ 2 D_ 3 were determined. Results Compared with the 3-month-old rats,the trabecular bone volume(TBV) of L4 and right tibiae decreased 43.3%( P