Lynch syndrome is the most common form of hereditary CRC, accounting for approximately 2~3% of population-based CRC. Individuals with Lynch syndrome have an increased risk for extracolonic cancer and second primary colorectal cancer. It has been dedicated that Lynch syndrome is an autosomal dominant cancer predisposition syndrome caused by germline mutations in the DNA mismatch repair genes (MMR)—MLH1, MSH2, MSH6 and PMS2, and EPCAM mutation is also found associated with MSH2 deficiency recently. Even though clinical diagnostic criteria (Amsterdan I/II, revised Bethesda) have been released decades ago, molecular testing of MMR genes is still the golden standard of Lynch syndrome diagnosis. Colorectal cancer patients less than 70y, are recommended to get into the procedure of Lynch syndrome screening, starting with microsatellite instability and/or immunohistochemical analysis on the tumor specimen followed by germline genetic testing and possibly further studies, such as MLPA. Notably, Testing on BRAF mutation is necessary, when the expression of MLH1 is lost, in order to exclude the sporadic colorectal cancer. Individuals with identified germline mutations need further screening for their immediate relatives.