Systemic immune-inflammation index (SII), on the basis of lymphocyte, neutrophil and platelet counts had been published to be a good prognostic factor in multiple cancers. Nevertheless, the prognostic value of SII in cancer patients remains inconsistent. Therefore, we carried out a meta-analysis to evaluate the prognostic value of SII in these patients with cancer. A total of 22 articles with 7657 patients enrolled in this meta-analysis. The combined result revealed that a high SII was evidently correlated with poor overall survival (OS) (HR=1.69, 95%CI=1.42-2.01, p<0.001), poor time to recurrent (TTR) (HR=1.87, p<0.001) , poor progress-free survival (PFS) (HR=1.61, p=0.012) ,poor cancer-specific survival (CSS) (HR=1.44, p=0.027) , poor relapse-free survival (RFS) (HR=1.66, p=0.025) and poor disease-free survival (DFS) (HR=2.70, p<0.001) in patients with cancers. Subgroup analysis indicated that SII over the cutoff value could predict worse overall survival in Hepatocellular carcinoma (p<0.001), Gastric cancer (p=0.005), Esophageal Squamous Cell Carcinoma (p=0.013), Urinary system cancer (p<0.001), Small cell lung cancer (p<0.001), Non-Small cell lung cancer (p<0.001) and Acral Melanoma (p<0.001). The largest effect size was observed in the Hepatocellular carcinoma (HR=2.11). In addition, these associations did not vary significantly by the cutoff value, sample size and ethnicity. Therefore, high SII may be a potential prognostic marker in patients with various cancers and associated with the poor overall outcomes.