SUMMARYLynch syndrome is an autosomal dominant genetic disease characterized by the early onset of colon cancer, endometrial cancer and other tumors caused by a genetic mutation within DNA mismatch repair (MMR) genes. A small subgroup (approximately 3%-5%) of endometrial cancer and colorectal cancer is related to Lynch syndrome. Identification of these patients in clinical practice will be of great benefit to the relatives and patients themselves. We reported two cases, and reviewed the literature and clinical diagnostic guideline. MMR protein was lost in the tumors. Meanwhile the two cases had different clinicopathological characteristics. Together with the literature, our findings may suggest that the MMR protein expression, associated molecular alterations and clinicopathological features and biological behavior of endometrial cancer and colorectal cancer related to Lynch syndrome are different. Thus the algorithm for detection the patients at highest risk is different. To detect the MMR loss by immunohistochemistry is a practicalscreening method.