Abstract: Objective 　To explore the relationship between expression of KAI1 gene and the genesis and development of colorectal cancer (CRC) . Methods 　The expression of KAI1 mRNA and protein were respectively detected using RT-PCR and high sensitive Envision^TM immuno-histochemical method in 40 cases of CRC, 8 cases of t ransitional mucosa and 8 cases of normal mucosa. Results 　The KAI1 mRNA of normal mucosa was significantly lower than that of tumor ( P < 0. 05), and there was no difference between the normal mucosa and the transitional mucosa on statistics although the KAI1 mRNA of latter was higher slightly than that of the former. The positive cases of KAI1 protein in primary CRC were 25 (62. 5 %), weak cases were 9 (22. 5 %), negative cases were 6 (15 %) . KAI1 mRNA and protein expression reduced in the cases of low differentiation and the cases with lymph node metastasis ( P < 0. 01, P <0. 01 ; P < 0. 05, P < 0. 05) . Conclusion 　The abnormal expression of KAI1 probably participates in genesis and development of CRC, and possesses clinical significance in evaluating the differentiation, lymph node metastasis of CRC.