Purpose: The clinical implication of p53 mutation in gastric cancer is still unclear, as shown by the discordant results that continue to be reported in the literature. Materials and Methods: To assess p53 gene mutation, tumor p53 overexpression, and serum anti-p53 antibody, we employed a polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis, an immunohistochemistry using monoclonal antibody DO-7, and an enzymelinked immunosorbent assay (ELISA), respectively. Results: Of 169 surgical specimens of gastric cancer, mutation at exon $5∼8$ of the p53 was identified in 33 ($19.5\%$) and was significantly correlated with lymph node metastasis. Overexpression of p53 was found in 62 specimens ($36.7\%$) and had a significant correlation with tumor differentiation. Serum anti-p53 antibody was positive in 18 patients ($10.7\%$). Twenty-three of the mutated tumors ($69.7\%$) and 39 of the non-mutated tumors ($28.7\%$) displayed immunoreactivity. Twelve of the immunopositive tumors ($19.4\%$) and 6 of the immunonegative tumors produced anti-p53 antibody. These differences were statistically significant (P<0.001 and P=0.005, respectively). There was no significant difference in survival according to the mutation of p53. Conclusion: Mutation and overexpression of p53 can be easily detected by immunohistochemistry. However, standardization of the immunohistochemical staining method, as well as guidelines for interpreting the stained result, will produce concordant results and thereby improve clinical application.