To compare the diagnostic value of [68Ga]Ga-FAP-2286 PET/CT and [18F]-FDG PET/CT imaging in different types of pleural/peritoneal metastatic tumors.A retrospective analysis was conducted on patients who underwent both [18F]-FDG and [68Ga]Ga-FAP-2286 PET/CT in our department between January 2022 and November 2024. The maximum standardized uptake value (SUVmax), peak SUV (SUVpeak), and tumor-to-background ratio (TBR) of pleural/peritoneal metastatic lesions were measured, and the results obtained from the two imaging modalities were compared.A total of 92 patients suspected of having pleural/peritoneal metastases were included in the study. The [68Ga]Ga-FAP-2286 PET/CT showed higher SUVmax, SUVpeak, TBR, and sensitivity compared to [18F]-FDG PET/CT (7.87 vs. 6.28; P = 0.002; 5.88 vs. 4.65; P < 0.001; 6.27 vs. 3.85; P < 0.001; 95.3% vs. 84.7%; P = 0.035), especially for peritoneal metastases (8.25 vs. 5.75; P < 0.001; 6.18 vs. 4.29; P < 0.001; 6.54 vs. 3.50; P < 0.001). Among various tumors, [68Ga]Ga-FAP-2286 PET/CT showed better detection results for hepatobiliary and pancreatic tumors (7.88 vs. 6.02, 5.88 vs. 4.33, 6.15 vs. 3.67), gastrointestinal tumors (8.27 vs. 5.69, 6.28 vs. 4.30, 7.03 vs. 3.50), and adenocarcinomas (8.30 vs. 5.80, 6.17 vs. 4.30, 6.60 vs. 3.55).For pleural/peritoneal metastases, [68Ga]Ga-FAP-2286 PET/CT has a higher detection rate compared to [18F]-FDG PET/CT, providing better diagnostic efficacy, particularly for peritoneal metastases. Among various tumors, [68Ga]Ga-FAP-2286 PET/CT has higher diagnostic value in hepatobiliary and pancreatic tumors, gastrointestinal tumors, and adenocarcinomas.© 2025. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.