Objective To detect expression of Ras association domain family 1A （RASSF1A） gene in the colonic carcinoma tissue and to analyze the relationship of this expression to its clinical features. Methods Immunohistochemistry and Western blot methods were employed for detecting the RASSF1A protein expressions in 34 colonic carcinoma tissues and corresponding normal colon tissues. RT-PCR was employed for detecting RASSF1A mRNA expression. Results ①The RASSF1A protein expression in the colonic carcinoma tissues was significantly lower than that in the normal colontissues by using immunohistochemistry〔35.3% （12/34） versus 97.1% （33/34）， P＜0.05〕.There were significant relati-onships of RASSF1A protein expressions to the tumor differentiation and TNM stage （P＜0.05）， in other words， the positive rates of RASSF1A protein in the moderately and well differentiated andⅠ＋Ⅱof TNM colonic carcinoma tissues were all higher （P＜0.05）. ② The RASSF1A protein expression in the colonic carcinoma tissues was significantly lower than that in the normal colon tissues by using Western blot 〔0.316 8±0.019 6 versus 0.914 4±0.177 6， P＜0.05〕， which was close to the result of RT-PCR〔0.158 9±0.223 7 versus 0.572 3±0.193 9， P＜0.05〕. Conclusions Absentexpre-ssion of RASSF1A gene in the colonic carcinoma tissue might play an important role in tumor genesis and tumor progre-ssion， and it might become useful early detection of the colonic carcinoma.