Objective To determine the effect of different doses vitamin D supplementation to the change of bone metabolism in 6 months after Roux-en-Y gastric bypass ( RYGB) .Methods The change of body weight and body mass index ( BMI ) in 36 patients in 6 months after RYGB WAS analyzed.Then,the effect of low-dose (n=11,400 IU/day) and high-dose (n=12,1 600 IU/day) vitamin D to the serum calcium,25-hydroxyvitamin D and bone density were observed ,and 15 patients as control .Results In 6 months after RYGB,the body weight and BMI were decreased ,and the differences were statistical significance (P<0.05).The serum calcium,25-hydroxyvitamin D and bone density were increased in high-dose group,and the differences were statistical significance (P<0.05).Conclusion High-dose (1 600 IU/day) vitamin D supplementation is effective to the bone loss of patients undergoing RYGB .