Interleukin-17A (IL-17A) and IL-17F play a role in tissue inflammation by inducing release of proinflammatory and neutrophil-mobilizing cytokines. We investigated the associations between gastric cancer and polymorphisms of IL-17A (rs2275913, G-197A) and -17F (rs763780, 7488 T/C) genes. The study was performed in 811 subjects (524 without gastric cancer and 287 with gastric cancer). We used the multiplex PCR-SSCP method to detect gene polymorphisms. Overall, the number of IL-17A/-197A allele was significantly correlated to the development of gastric cancer (OR, 1.42; 95% CI, 1.09-1.85; p = 0.010). The frequency of IL-17A/-197 A/A homozygote was also significantly higher in gastric cancer group than in non-cancer group (OR, 3.02; 95% CI, 1.86-4.91; p < 0.0001). The IL-17A/G-197A polymorphism was more closely correlated to intestinal-type cancer than diffuse-type cancer. In addition, IL-17A/-197A allele carriers had an increased risk of the development of gastric mucosal atrophy (OR, 1.68; 95% CI, 1.06-2.65; p = 0.026), and a positive relationship between the inflammation score and the number of -197A allele was observed (p = 0.022). We concluded that G-197A polymorphism of IL-17A gene was significantly associated with the development of gastric cancer, especially intestinal-type cancer.