Although several clinical trials studied the efficacy of chitosan on weight loss, controversial results have been found. Herein, we evaluated randomized controlled trials (RCTs) of chitosan consumption in adult participants on body weight and body composition through a meta-analysis with trial sequential analysis (TSA). We searched EMBASE, MEDLINE, Web of Science, and CENTRAL databases. The primary body composition indices including body weight, body mass index (BMI), waist circumference, body fat, and hip circumference were extracted. The quality of included articles was assessed according to the Cochrane risk of bias tool. Data were pooled using the random-effects models and calculated as weighted mean difference (WMD) with 95% confidence intervals (CI). Heterogeneity investigated using I2 statistics. TSA, subgroup analyses, sensitivity analysis, meta-regression and publication bias were also evaluated. Overall, 15 eligible trials (18 treatment arms) with 1130 subjects were included. The pooled analyses revealed a significant reduction in body weight (WMD, -0.89 kg; 95% CI, -1.41 to -0.38; P = 0.0006), BMI (WMD, -0.39 kg/m2; 95% CI, -0.64 to -0.14; P = 0.002) and body fat (WMD, -0.69%; 95% CI, -1.02 to -0.35; P = 0.0001) receiving chitosan supplementation. Subgroup analyses also showed that consuming chitosan in dose (>2.4 g/d), shorter-term (<12 weeks), studies with parallel design and studies including participants with obese or overweight had positive effects on body composition. TSA provided conclusive evidence for the benefit of chitosan supplementation. Our findings provided evidence that chitosan consumption might be a useful adjunctive pharmacological therapeutic tool for body weight management particularly in overweight/obese participants. Further well-constructed clinical trials that target body weight and body composition as their primary outcomes are needed.