To explore the expression and function of MG 7 Ag on gastric cancer cell line SGC7901 and its drug resistant subline,SGC7901/VCR, with different resistance index (0 3, 0 7, 1 0) The expression of MG 7 Ag on SGC7901 and SGC7901/VCR cells was determined by immunohistochemical method and flow cytometry (FCM) MTT assay was used to explore the effects of monoclonal antibody MG 7 on drug sensitivity of gastric cancer cells FCM was used to explore the effects of MG 7 on adriamicine accumulation of SGC7901/VCR cells SGC7901/VCR cells exhibit increasing positive staining of MG 7 than SGC7901, according to the increasing resistance index Sensitivity of vincristine of both SGC7901 and SGC7901/VCR cells was reduced after being treated with MG 7 And SGC7901/VCR cells showed decreased adriamicine accumulation when they were incubated with MG 7 Therefore, the conclusion is that MG 7 Ag may be a novel molecule associated with multidrug resistance of gastric cancer, and play an important role in maintaining the drug resistant phenotype of SGC7901/VCR cells.