Purpose Usefulness of FDG PET-CT in monitoring response in locally advanced gastric cancer has been reported. The purpose of this study was to evaluate the related factors to detect measurable diseases in advanced gastric cancer on FDG PET-CT. Methods We retrospectively reviewed 38 patients diagnosed as having advanced gastric cancer. We defined the measurable diseases when there was visualized tumor of which maximum standardized uptake value (SUVmax) was higher than $1.35^*SUVmax$ of liver + $2^*SD$ of liver SUV. We evaluated what kinds of factors from the clinicopathologic features were related to identifying measurable diseases. Results Of 38 patients with advanced gastric cancer, 18 (50 %) had measurable tumors on FDG PET-CT. Measurable tumors were significantly more frequent in well or moderately differentiated adenocarcinoma (70.5 % vs 35.3 %, p<0.05), in the tumors located at antrum or angle (66.7 % vs 29.4 %, p<0.05) and in the elderly group (age of 55 years old or more, 72.0 % vs 8.3 %, p<0.001) than the others, respectively. By multivariate analysis, age at diagnosis was the only independent predictor for the measurable disease on FDG PET-CT. Conclusion We found that age at diagnosis, as well as histologic types and location of tumors, were the affecting factors to detect measurable disease on FDG PET-CT in patients with advanced gastric cancer. Our study suggests that elderly patients of age of 55 years old or more can frequently have T-measurable disease on FDG PET-CT in advanced gastric cancer and FDG PET-CT will be helpful to monitor measurable disease.