Cellular prion protein (PrP^C), a glycosylphosphatidylinositol-anchored membrane protein, was found in our lab to be widely expressed in gastric cancer cell lines. In order to evaluate its biological significance in human gastric cancer, we investigated its expression in a large series of gastric tissue samples (n = 124) by immuno histochemical staining with the monoclonal antibody 3F4. Compared with normal tissues, gastric adenocarcinoma showed increased PrP^C expression, correlated with the histopathological differentiation (according to the WHO and Lauren classifications) and tumor progression (as documented by pTNM staging). To better understand the underlying mechanism, we introduced the PrP^C and two pairs of RNAi into the poorly differentiated gastric cancer cell line AGS and found that PrP^C suppressed ROS and slowed down apoptosis in transfected cells. Further study proved that the apoptosis-related protein Bcl-2 was upregulated whereas p53 and Bax were downregulated in the PrP^C-transfected cells. A reverse effect was observed in PrP^C siRNA-transfected cells. These results strongly suggested that PrP^C might play a role as an effective antiapoptotic protein through Bcl-2-dependent apoptotic pathways in gastric cancer cells. Further study into the mechanism of these relationships might enrich the knowledge of PrP, better our understanding of the nature of gastric carcinoma, and further develop possible strategies to block or reverse the development of gastric carcinoma.