Lewis(y) antigen is an oligosaccharide containing two fucoses, and is expressed variously in 75% of ovarian tumors, where its high expression level predicts poor prognosis. The effect and the possible mechanism of Lewis(y) on the proliferation of human ovarian cancer cells are still largely unkown. We report here that transfecting alpha1,2-FT gene into RMG-I cells increased the expression of Lewis(y) and promoted cell proliferation. In alpha1,2-FT-transfected cells, the Lewis(y) content of EGFR was increased dramatically. Tyrosine phosphorylation of EGFR was elevated. Concomitantly, tyrosine phosphorylation of Akt, ERK1/2 was also upregulated. Moreover, the expression of HER2/neu mRNA and protein, the tyrosine phosphorylation of HER2/ neu were also elveated, while the expression of p27 was significantly reduced. However, the expression of EGFR and the relative content of Lewis(y) on HER2/neu were unchanged. The above-mentioned alterations were correlated with the Lewis(y) content of EGFR and alpha1,2-FT expression in cells. In addition, the phosphorylation intensity and difference in phosphorylation intensity between cells with different expression of alpha1,2-FT were attenuated significantly by the inhibitor of EGFR tyrosine kinase and by the mono-antibody to Lewis(y). Meanwhile, the reduction in p27 and the difference in its expression among the two cell lines were also blocked by the Lewis(y) antibody. The PI3K signaling pathway was more important than the MAPK pathway in the regulation of p27 expression. These findings provide strong evidence that increased expression of Lewis(y) promotes cell proliferation through regulating the phosphorylation and expression of some molecules involved in the EGFR/PI3K-signaling pathway.