Objective: To study the expression of tumor-infiltrating lymphocytes (TIL) and their prognostic roles in colorectal cancer. Methods: The colorectal cancer specimens from the patients who had been operated in our hospital over a past 16-year period were collected, with 30 cases of either survival time≥5 years or ≤3 years.Immunohistochemical staining and flow cytometry were used to detect the expression of tumor-infiltrating CD4 and CD8 T lymphocyte, and the relations of their expressions with clinicopathological features and prognosis were analyzed. Results: The expression rate of CD4 and CD8 in colorectal cancer tissues was 28.3% (17/60) and 41.6%(25/60)by immunohistochemical staining, respectively. The expression levels of CD4 and CD8 in cancer nests were significantly lower than those in interstitial tissue (both P＜0.05).The expression of CD4 and CD8 in tumor tissue was irrelevant to gender,age,lymph node metastasis and differentiation degree of tumor, and was correlated with tumor Dukes stage and outcome of the patients. The expression rates of CD4 and CD8 in the patients with Dukes stage A+B cancer were both higher than those in the patients with Dukes stage C+D cancer, and the expression rates of CD4 and CD8 in the patients with survival time ≥5years were both significantly higher than those of the patients with survival time ≤3 years(both P＜0.05). Flow cytometry analysis showed that the CD4/CD8 ratio of tumor-infiltrating lymphocytes was related to the Dukes stage and outcome of the patients (P＜0.05). Conclusions: Tumor-infiltrating CD4 and CD8 T lymphocyte can be used as the prognosis factors for patients with colorectal cancer, and low infiltration of TIL in tumor regions predicts a poor prognosis.