Abstract: To examine the variation in the antigen CD44 when immuno-conjugated with the monoclonal antibody KMP1 and the biological effects of KMP1 on EJ cells. Methods: KMP1, the antibody against bladder cancer that could recognize the aberrantly glycosylated CD44 of human EJ cells, was obtained from BALB/c mice. ELISA was used to determine the affinity, binding site, and valence of this antibody. Flow cytometry and immunohistochemistry were conducted to detect the specificity of this antigen on the EJ cells and cancer tissues. The specific antigen was separated and purified by affinity chromatography, and its amino acid sequence was determined. After glycosyltransferase inhibition by benzyl-N-acetyl-d-galactosaminide ( BG ) and mild periodate oxidation, the variation in the physico-chemical property of the antigenic determinant was analyzed. Soft agar clone formation and wound healing assays were performed to investigate the effect of KMP1 on the proliferation and migration of the EJ cells. Results: KMP1 was an IgG1 antibody that can be specifically bound to the EJ, BIU-87, and T24 cell lines as well as to bladder carcinoma tissue, but not to the Lovo, HeLa, K562, HepG2, Jurkat, 293, HCV29 cell lines, the human red blood cell, human lymphocytes, or normal bladder tissue. KMP1 recognizes aberrantly glycosylated CD44 of EJ cells. BG inhibited the conjugation of KMP1 and EJ cells. KMP1 inhibits cancerous proliferation and migration of the EJ cells. Conclusions: The high recurrence and metastasis of the bladder carcinoma may be in a definite relation to the high expression of CD44 with aberrant glycosylation. KMP1 can bind the aberrantly glycosylated CD44 and inhibit the proliferation and migration of the EJ cells.