Objective To detect expression of CK20 mRNA in peripheral blood of patients with colorectal carcinoma and its clinical significance. Methods Using the reverse transcriptase-polymerase chain reaction (RT-PCR),CK20 mRNA expression was examined in peripheral blood from 42 patients with colorectal carcinoma before and after operation, 20 healthy volunteers, 20 fresh colorectal carcinoma samples. Results The positive expression rates of CK20 mRNA were 45.24%(19/42) and 33.33%(14/42) before and after operation in 42 colorectal carcinoma patients respectively. All 20 fresh colorectal carcinoma samples revealed expression of CK20 mRNA, but the 20 normal blood samples did not. Conclusion The detection of CK20 mRNA in peripheral blood is helpful to early diagnose, assess the prognosis and make a correct treatment of colorectal carcinoma.