Hemiplegic shoulder pain and impairment are common poststroke outcomes, for which arm slings constitute long-used treatments. Although multiple studies have suggested association between gait pattern and sling application, results have varied. Accordingly, we conducted this meta-analysis to determine how arm sling use affects the gait and balance of patients with poststroke hemiplegia. The PubMed, Embase, and Cochrane Library databases were searched until April 21, 2021, for randomized or quasi-randomized controlled trials evaluating the effect of arm slings on gait or balance in patients with poststroke hemiplegia. The primary outcome was walking speed; the secondary outcomes were functional balance tests or walking evaluation parameters for which sufficient analytical data were available in three or more studies. Nine studies with a total of 235 patients were included, all of which were within-patient comparisons. Six studies reported significant between-group differences in walking speed with and without the use of arm slings. Patients wearing arm slings had higher walking speed (standardized mean difference = − 0.31, 95% confidence interval [CI] = − 0.55 to − 0.07, P = 0.01, n = 159; weighted mean difference = − 0.06, 95% CI − 0.10 to − 0.02, P = 0.001, n = 159). Our findings suggest that arm sling use improves gait performance, particularly walking speed, in patients with poststroke hemiplegia.