Here, we found that ARNT and MDR1 were significantly up-regulated in SGC7901/ADR and SGC7901/VCR cell lines compacared to SGC7901, the effect of significant up-regulation of MDR1 mediated by ARNT expression vector transfection was compromised via Sp1 siRNAs transfection, which indicated the role of ARNT-MDR1pathway in the MDR phenotype of gastric cancer. Here, SP1 is linked to gastric cancer.