Abstract: Objective 　To develop a nested reverse t ranscriptase polymerase chain reaction method to amplify Cytokeratin 20mRNA and Matrix Metalloproteinase-7mRNA for detecting colorectal cancer micro-metastases in lymph nodes . Methods 　The RT-PCR system was set up by using nest primer. The presence of CK20 mRNA and MMP-7 mRNA was investigated by nested RT-PCR in 100 lymph nodes from 30 colorectal cancer patients who underwent curative operation. Tweenty-five lymph nodes f rom 10 patients with benign intestinal disease were served as negative control. The result s of nested RT-PCR were compared with ones of routine histology. Results 　The positive rate of CK20 mRNA and MMP-7 mRNA in 187 lymph nodes from 30 colorectalcancer patient s was 40. 11 %(75/ 187), 51. 87 %(97/ 187) respectively, while only 57 samples were histologically positive. The expression of CK20 mRNA and MMP-7 mRNA in 25 lymph nodes of 10 cases of cont rol group were all negative. Conclusion 　Nested reverse transcriptase polymerase chain reaction was a sensitive and specific method to indicate the expression of CK20 mRNA and MMP-7 mRNA in lymph nodes as a helpful marker of micrometastases of colorectal carcinoma cells. It is superior to routine histopathological assay in examing lymph node metastases. The detection of CK20 mRNA and MMP-7 mRNA in lymph nodes may cont ribute to improve the accuracy of clinical staging, determine patient s' prognosis and provide information for adjuvant therapy.