Objective To systematically evaluate the correlation between the expression of microRNA (miRNA)-21 and the prognosis of esophageal cancer. Methods PubMed, Cochrane Library, Embase, Wanfang Data, China National Knowledge Infrastructure and VIP Databases were searched by for the literature on the correlation between miRNA-21 and the prognosis of esophageal cancer till July 10, 2022. Two researchers independently performed literature screening, quality evaluation, and data extraction. Statistical analysis was conducted with Stata 14.0. Results A total of 13 articles were included, including 1 204 patients. The results of meta-analysis showed that: the overall survival (OS) of patients with high expression of miRNA-21 was lower than that of patients with low expression of miRNA-21 [hazard ratio (HR)=2.11, 95% confidence interval (CI) (1.56, 2.84), P<0.001]. miRNA-21 expression was not associated with disease free survival [HR=2.53, 95%CI (0.67, 8.22), P=0.182]. The OS of Asian patients with high expression of miRNA-21 was significantly lower [HR=2.44, 95%CI (1.71, 3.49), P=0.005], while the OS of non-Asian patients was not related to miRNA-21 expression [HR=1.34, 95%CI (0.94, 1.91), P=0.363]. The high expression of miRNA-21 was correlated with the decreased OS in patients with esophageal squamous cell carcinoma [HR=2.22, 95%CI (1.52, 3.26), P=0.001], while the OS in patients with esophageal adenocarcinoma was not correlated with the expression of miRNA-21 [HR=1.39, 95%CI (0.63, 3.06), P=0.409]. Conclusion The overexpression of miRNA-21 is associated with poor prognosis and might be regarded as a potential prognostic biomarker for patients with esophageal cancer.