Background: To date, several studies have been carried out on the association of TNF-a -308G>A with the risk of cervical cancer (CC) and breast cancer (BC). However, their conclusions were not consistent. Thus, we performed a comprehensive meta-analysis to evaluate the association more precisely from all eligible case-control studies. Methods: We searched the PubMed, Google Scholar and Cochrane Library databases systematically to identify relevant studies up to 1 February 2019. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using a fixed-or random-effects model. Results: A total of 40 case-control studies including 20 studies with 4,780 cases and 4,620 controls on CC and 20 studies with 12,390 cases and 14,910 controls on BC were selected in this meta-analysis. The pooled results showed that the TNF-a -308G>A polymorphism was significantly associated with an increased risk of CC (A vs. G: OR 1.277; 95% CI 1.104–1.477; P = 0.001; AA vs. GG: OR 1.333; 95% CI 1.062–1.674; P = 0.013; AG vs. GG: OR 1.307; 95% CI 1.064–1.605; P = 0.011; and AA + AG vs. GG: OR 1.324; 95% CI 1.104–1.587; P = 0.002) and BC (AA vs. AG + GG: OR 0.094; 95% CI 0.058–0.152; P ≤ 0.001). In the stratified analyses by ethnicity, the TNF-a -308G>A polymorphism was significantly associated with the risk of CC (in Caucasians and Africans) and BC (Caucasians and Asians). Conclusion: Our findings showed that TNF-a -308G>A polymorphism may be a risk factor for cervical cancer and breast cancer overall and by ethnicity.