Abstract: Objective 　To detect the expression of the terminal Galbeta1-4 GlcNAc related polysa- ccharide in serum of nasopharyngeal carcinoma, primary liver cancer, and colorectal cancer and lung cancer patients. Methods 　The RCA Ⅰidentifying Terminal Galβ1-4 GlcNAc glycoprotein was acquired by RCA Ⅰ(Ricinus communis agglutinin Ⅰ) affinity chromatography method f rom normal person serum and was marked by the horseradish peroxidase. 133 tumor patient s, 64 benign disease patient s and 240 normal person serums were detected by the subt raction of agglutinin. Results 　The polysaccharide level of the RCAⅠidentification in serum of nasopharyngeal carcinoma, primary liver cancer and colorectal cancer was obvious higher than it in normal person and benign disease patient s. The positive rate was 66. 7 %, 73. 9 % and 64. 9 % relatively. Lung cancer had only positive rate 19. 4 %. After effective therapy, the polysac-charide lever of the RCA Ⅰidentification in serum of nasopharyngeal carcinoma and colorectal cancer remarkably descent, the positive rate also descent . Conclusion 　The terminal Galbeta124 GlcNAc related polysac-charide in serum can be applied to the research of abnormal polysaccharide in tumor patient and pathogenesis. It s level can provide reference for clinical diagnosis and the evaluation on curative effect .