Purpose: We investigated whether PET radiomic features are affected by differences in the scanner, scan protocol, and lesion location using 18F-FDG PET/CT and PET/MR scans. Results: SUV, TMR, skewness, kurtosis, entropy, and homogeneity strongly correlated between PET/CT and PET/MR images. SUVs were significantly higher on PET/MR0-2 min and PET/MR0-10 min than on PET/CT in gynecological cancer (p = 0.008 and 0.008, respectively), whereas no significant difference was observed between PET/CT, PET/MR0-2 min, and PET/MR0-10 min images in oral cavity/oropharyngeal cancer. TMRs on PET/CT, PET/MR0-2 min, and PET/MR0-10 min increased in this order in gynecological cancer and oral cavity/oropharyngeal cancer. In contrast to conventional and histogram indices, 4 textural features (entropy, homogeneity, SRE, and LRE) were not significantly different between PET/CT, PET/MR0-2 min, and PET/MR0-10 min images. Conclusions: 18F-FDG PET radiomic features strongly correlated between PET/CT and PET/MR images. Dixon-based attenuation correction on PET/MR images underestimated tumor tracer uptake more significantly in oral cavity/oropharyngeal cancer than in gynecological cancer. 18F-FDG PET textural features were affected less by differences in the scanner and scan protocol than conventional and histogram features, possibly due to the resampling process using a medium bin width. Methods: Eight patients with gynecological cancer and 7 with oral cavity/oropharyngeal cancer underwent a whole-body 18F-FDG PET/CT scan and regional PET/MR scan in one day. PET/MR scans were performed for 10 minutes in the list mode, and PET/CT and 0-2 min and 0-10 min PET/MR images were reconstructed. The standardized uptake value (SUV), tumor-to-muscle SUV ratio (TMR), skewness, kurtosis, entropy, homogeneity, short-run emphasis (SRE), and long-run emphasis (LRE) were compared between PET/CT, PET/MR0-2 min, and PET/MR0-10 min images.