Effect of glycosylation modification on the shape of microvillus was investigated on rat liver epithelial cell line WB-F344. Since rat ER alpha-mannosidase has 89% identity to human 6A8 alpha-mannosidase, we used an antisense 6A8 cDNA fragment to inhibit expression in WB-F344 cells. Cells were transfected with antisense 6A8, the relevant sense fragment or the mock plasmid. Genomic PCR for neo(R) demonstrated integration of the transfected gene into host DNA. Enzymatic activity assay on p -nitro-phenyl-alpha-D-mannopyranoside showed suppression of ER alpha-mannosidase expression in the cells transfected with antisense 6A8. Concanavalin A binding to these cells was enhanced, indicating a modification in glycosylation. Number reduction and blunting of microvillus on these cells was observed. Transduction with the sense fragment or the mock had no effect. Cells with suppressed ER alpha-mannosidase expression grew slower in culture. Our results indicate an obvious effect of glycosylation modification on microvilli, which might be related with malfunctioning of cells.