Objective To compare ratio of circulating Th17 over Tc17 cells in patients with colorectal polyp (CRP), colorectal adenoma (CRA) and colorectal cancer (CRC),and analyse their relationship. Methods The ratio of circulating Th17 over Tc17 cells in 93 patients(17 CRP, 34 CRA and 42 CRC)and 17 healthy donors were examined by flow cytometry;Serum levels of IL-17A and IL-23 were tested by ELISA. Results The ratio of circulating Th17 over Tc17 cells and the se-rum levels of IL-17A and IL-23 were the lowest in healthy control groups, medium in CRP and CRA groups and the highest in CRC groups (P＜0.05). The proportions of Tc17 cells in CRA groups were significantly higher compared to those in CRP groups,but no statistical significance of proportion of circulating Th17 cells as well as serum levels of IL-17A and IL-23 be-tween CRA and CRP groups was observed (P>0.05). Further analysis showed that there was a positive correlation between proportions of circulating Th17 and Tc17 cells (rs=0.594, P＜0.001). Conclusion The proportions of circulating Th17 and Tc17 cells were positively related and the ratio of Th17 over Tc17 was markedly increased from CRP group or CRA group to CRC group.