Background: An effective method to explore pathophysiological mechanisms and related biological markers of Alzheimer's disease (AD) is required. Multiple studies have revealed that local complement activation occurs in the brains of patients with early-stage AD. The goal of this study was to compare the concentrations of complement C3 in the cerebrospinal fluid (CSF) of patients with AD and healthy elderly controls (HC). Methods: The PubMed, Web of Science, Cochrane Library, and Embase databases were searched for original studies that evaluated the association between complement C3 and AD. Finally, 4 studies were included. Stata 11.0 and RevMan 5.4 software were used for meta-analysis. The Egger’s test was used to assess publication bias. Results are expressed as the standardized mean difference (SMD) with 95% confidence interval (CI). Results: The heterogeneity test result of C3 levels in the cerebrospinal fluid of patients with AD vs. healthy controls was (Q=14.47, P=0.002, I2=79%). It was considered that the heterogeneity among the studies was not small; therefore, a random-effects model was used for analysis. The combined value of the estimated effect was [SMD=0.39, 95% CI (0.01, 0.77); P=0.04]. The sensitivity analysis indicated that no study had a remarkable influence on the results of the pooled estimate. Egger's test was used to test the bias (Egger's test, t=-0.75; P=0.532 > 0.050). Conclusion This meta-analysis found that C3 levels in the cerebrospinal fluid of patients with Alzheimer's disease were significantly higher than those in healthy controls.