Objective:To investigate the expression and significance of programmed death ligand 1 (PD-L1) and programmed death 1 (PD-1) in colorectal cancer complicated by schistosomiasis.Methods:A total of 134 patients with colorectal cancer who received treatment in Xuancheng People's Hospital during 2014-2021 were included in this study. These patients consisted of 74 patients with colorectal cancer combined with schistosomiasis (patient group) and 60 patients with only colorectal cancer (control group). The expression of PD-L1 and PD-1 in colorectal cancer tissue was detected by an immunohistochemical method. The differences in PD-L1 and PD-1 expression were compared between the two groups. The relationships between PD-L1 and PD-1 expression and clinical pathological characteristics were determined.Results:The positive expression rates of PD-L1 and PD-1 in cancer cells and interstitial lymphocytes were 55.4% and 60.8% respectively in the patient group and they were 35.0% and 40.0% respectively in the control group. The positive expression rates of PD-L1 and PD-1 were significantly higher in the patient group than the control group ( χ2 = 5.55, 5.74, both P < 0.05). The expressions of PD-L1 and PD-1 in the patient group were correlated with lymph node metastasis and high tumor-node-metastasis stage ( P < 0.05). Conclusion:PD-L1 and PD-1 are highly expressed in colorectal cancer complicated by schistosomiasis and are related to their invasive behavior. PD-1/PD-L1 singaling pathway may be involved in the molecular mechanism underlying the occurrence and development of colorectal cancer complicated by schistosomiasis. Blocking PD-1/PD-L1 signaling pathway may be a new strategy for immunotherapy of colorectal cancer complicated by schistosomiasis.