This study aimed to compare the performance of [ 68 Ga]Ga-DOTA-FAPI-04 and [ 18 F]FDG PET/CT in the evaluation of primary and metastatic lesions of gastric cancer. Fifty-six patients with histologically proven gastric carcinomas were enrolled in this study, including 45 patients for staging and 11 patients for restaging after surgery. Each patient underwent both [ 18 F]FDG and [ 68 Ga]Ga-DOTA-FAPI-04 PET/CT within 1 week. The activity of tracer accumulation in lesions was assessed by maximum standardized uptake value (SUV max ) and TBR (lesions SUV max /ascending aorta SUV mean ). Histological workup served as a standard of reference. If tissue diagnosis was not applicable, the follow-up data including the results of laboratory tests and medical imaging could also serve as a reference. [ 68 Ga]Ga-DOTA-FAPI-04 PET/CT was comparable to [ 18 F]FDG on detecting primary tumors and lymph node (LN) metastases, whereas [ 68 Ga]Ga-DOTA-FAPI-04 outperformed [ 18 F]FDG in detecting peritoneal (159 vs. 47, P < 0.001) and bone metastases (64 vs. 55, P = 0.003) by the lesion-based analysis. [ 68 Ga]Ga-DOTA-FAPI-04 showed higher SUV max (10.3 vs. 8.1, P = 0.004) and TBR (11.6 vs. 5.8, P < 0.001) in primary tumor, and higher TBR in LN involvement (8.0 vs. 3.7, P < 0.001) and peritoneal metastases (8.1 vs. 3.2, P < 0.001), compared with [ 18 F]FDG PET/CT. The specificity and positive predictive value of [ 68 Ga]Ga-DOTA-FAPI-04 were significantly higher than that of [ 18 F]FDG (100.0% vs. 97.7%, P < 0.001; 100.0% vs. 57.1%, P = 0.001) in determining the LN status. [ 68 Ga]Ga-DOTA-FAPI-04 was comparable to [ 18 F]FDG in evaluating N-staging (47.1% vs. 23.5%, P = 0.282). [ 68 Ga]Ga-DOTA-FAPI-04 PET/CT detected more positive recurrent lesions in all restaging patients and showed clearer tumor delineation. Two patients underwent follow-up [ 68 Ga]Ga-DOTA-FAPI-04 PET/CT scans after chemotherapy, which both showed remission. [ 68 Ga]Ga-DOTA-FAPI-04 PET/CT can better evaluate primary gastric cancer and metastatic lesions in the peritoneu...