Aberrant expression of Lewis antigens has been demonstrated in gastric lesions, namely gastritis, intestinal metaplasia (IM) and gastric carcinoma (GC), and can be partly due to overexpression of the Lewis (FUT3) enzyme. Our aim was to evaluate the role of promoter methylation in FUT3 and Le(a) expression in gastric carcinoma cell lines. MKN45 cell line showed low amounts of Le(a), in the absence of FUT3; GP220 expressed high levels of Le(a) and FUT3. After 5aza-2'deoxycytidine MKN45 showed increased levels of FUT3 and Le(a), by immunohistochemistry and Real-Time PCR, whereas GP220 showed an increase in FUT3 without increase of Le(a). Enzyme activity assays confirmed an increase in alpha-1,4 fucosyltransferase activity in both cell lines by 5aza-2'deoxycytidine. Luciferase reporter gene assays, using methylated and unmethylated deletion constructs of FUT3 promoter, showed that FUT3 expression is regulated by methylation. Summing up, we showed that FUT3 overexpression in gastric cells depends upon promoter hypomethylation and that FUT3 is responsible for overexpression of Le(a) in gastric cells, in vitro. FUT3, Lea, Methylation.