Objective:To evaluate the effect of body mass index (BMI) on 24-hour urine compositions and blood biochemistries in patients with upper urinary tract calculi. Methods:A total of 119 of patients with upper urinary tract calculi were evaluated,and were classified as normal weight (18.5≤BMI<24.0,n = 37),overweight (24≤BMI<27,n = 52),or obese (27≤BMI,n = 30). The 24-hour urine sodium,potassium,calcium,phosphate,uric acid,serum sodium,potassium,calcium,phosphate,uric acid,and urine pH,and urine specific gravity were determined by biochemistry analyzer and were compared among the three groups. The proportion of metabolic disturbances was also compared among the three groups. Results:In male patients with stones,24-hour urine sodium,calcium,phosphate,uric acid and serum uric acid in obese and overweight groups were both significantly higher than those in normal group (P < 0.05). Urine pH in the obese group was significantly lower than that in overweight and normal groups (P < 0.05). Serum phosphate level in the overweight group was significantly higher than that in the normal group(P < 0.05). In female patients with stones,24-hour urine calcium,uric acid in the obese and overweight groups were both significantly higher than those in the normal group (P < 0.05). Urine pH in the obese and overweight groups were significantly lower than those in normal group(P < 0.05). Urine sodium in the obese group was significantly higher than that in normal group(P < 0.05). The proportion of hypersodiuria,hypercalciuria,hyperuricosuria and hyperphosphatemia and combined two or more metabolic disturbances in the obese group were significantly higher than those in normal group (P < 0.05). The proportion of hypersodiuria,hypercalciuria and combined two or more metabolic disturbances in the overweight group were significantly higher than those in the normal group(P < 0.05). The proportion of hypersodiuria and combined two or more metabolic disturbances in obese group were significantly higher than those in overweight group (P < 0.05). Conclusion: Obesity and overweight play a role in changes in 24-hour compositions,associated blood biochemistries and urine pH,and there is gender difference. A metabolic evaluation is necessary for stone patients,especially for obese and overweight ones,in treating and preventing urinary stones.