Soluble human leukocyte antigen-G (sHLA-G) has been reported in malignancies and is implicated in mediating immune surveillance of tumor. The aim of our study is to detect serum sHLA-G levels in colorectal cancer and to determine whether sHLA-G may be helpful in distinguishing colorectal cancer from benign colorectal diseases. Serum sHLA-G levels were determined using enzyme-linked immunosorbent assay. Receiver operating characteristic (ROC) curve was used to evaluate the feasibility of sHLA-G in differentiating colorectal cancer from benign colorectal diseases. Median sHLA-G concentrations were significantly higher in colorectal cancer compared to normal colorectum, hyperplastic polyp, inflammatory bowel disease and adenoma (all at p < 0.001, respectively). ROC curve for sHLA-G revealed an area under the curve of 84.2%, and when 88.6 U/mL was used as cutoff, a sensitivity of 72.2% and a specificity of 87.8% were achieved. Comparison of sHLA-G and carcinoembryogenic antigen ROC curves indicated that sHLA-G was superior to CEA in differentiating colorectal cancer from benign colorectal diseases (p < 0.001). ROC curves analysis of the combined sHLA-G and CEA showed a higher detection capacity (area under the ROC curve, 87.4%) than that of markers considered singly. These findings reveal that serum levels of sHLA-G are significantly increased in colorectal cancer which may serve as a potent mediator of immune escape in colorectal cancer, and sHLA-G may be a useful indicator in differentiating colorectal cancer from benign colorectal diseases.