Background: Whether calcium supplementation can reduce body weight and prevent obesity remains unclear because of inconsistent reports. Objective: We performed a meta-analysis to investigate the correlations between calcium supplementation and changes in body weight on the basis of age, sex, body mass index (BMI) of the subjects, and length of calcium intervention. Design: PubMed, EMBASE, Web of Knowledge, and China National Knowledge Infrastructure databases were systematically searched to select relevant studies that were published from January 1994 to March 2016. Both randomized controlled trials and longitudinal studies of calcium supplementation were included, and random- or fixed-effects models in a software program were used for the data analysis. Results: Thirty-three studies involving a total of 4733 participants were included in this meta-analysis. No significant differences in weight changes were shown between calcium intervention and control groups (mean: -0.01 kg; 95% CI - 0.02, 0.00 kg; P = 0.12). However, negative correlations between calcium supplementation and weight changes were shown in children and adolescents (mean: -0.26 kg; 95% CI: -0.41, -0.11 kg; P < 0.001) and in adult men and either premenopausal or old (>60 y of age) women (mean: -0.91 kg; 95% Cl: -1.38, -0.44 kg; P < 0.001) but not in postmenopausal women (mean: -0.14 kg; 95% CI: -0.54, 0.26 kg; P = 0.50). When BMI was considered, a negative correlation between calcium supplementation and weight changes was observed in subjects with normal BMI (mean: -0.53 kg; 95% CI: -0.89, -0.16 kg; P = 0.005) but not in overweight or obese subjects (mean: -0.35 kg; 95% CI: -0.81, 0.11 kg; P = 0.14). Compared with the control groups, no differences in weight changes were shown in the calcium-intervention groups when the lengths of calcium interventions were <6 mo (mean: -0.09 kg; 95% CI: -0.45, 0.26 kg; P = 0.60) or >= 6 mo (mean:-0.01 kg; 95% CI: -0.02, 0.01 kg; P = 0.46). Conclusion: Increasing calcium intake through calcium supplements can reduce body weight in subjects who have a normal BMI or in children and adolescents, adult men, or premenopausal women.