Background Postoperative sore throat negatively affects patient satisfaction and recovery. We conducted a systematic review and meta-analysis to examine the efficacy of preoperative topical administration of magnesium sulfate in preventing postoperative sore throat in adult patients. Methods We searched Medline, EMBASE, China National Knowledge Infrastructure, and the Cochrane Central Register of Controlled Trials from inception to 6 October, 2018. We included randomized-controlled trials that assessed the efficacy and safety of topical application of magnesium preoperatively in adult patients who underwent endotracheal intubation for general anesthesia. We then pooled the data using a random-effects model and conducted a trial sequential analysis on the incidence of sore throat. Our primary outcome was the incidence of sore throat at 24 hr after surgery/extubation. Our secondary outcomes included the severity of sore throat at 24 hr after surgery/extubation and adverse events. Results Eleven randomized-controlled trials involving 1,096 patients were included in this study. Topical application of magnesium was associated with reduced incidence of postoperative sore throat (risk ratio, 0.31; 95% confidence interval [CI], 0.21 to 0.45) as well as reduced severity of postoperative sore throat (standardized mean difference, - 2.66; 95% CI, - 3.89 to - 1.43). Three studies reported that significant adverse events were not associated with topical magnesium. The trial sequential analysis suggested that there is adequate evidence supporting the efficacy of topical magnesium in preventing postoperative sore throat. Conclusion Our study suggests that preoperative topical magnesium can effectively prevent postoperative sore throat.