To study the effects of exercise and weight control on bone mineral density (BMD) of girl athletes, dual X-ray and single X-ray absorptiometry were adopted to measure BMD; And serum Vitamin D3, estrogen, cholesterol and alkaline phosphatase levels of subjects were determined. Subjects were 63 students of two age groups (before puberty. 8-9 years old; after puberty: 15-16 years old, respectively) of sports and ordinary schools. The results showed that.. Exercise training is beneficial to increase BMD; Long term weight control had no effect on BMDof athletes in this study; Yet girl athletes after puberty with low estrogen levels had less BMD; Girl judo players with rapid weight loss had higher BMD as compared with the same aged nontraining students.