Abstract: Objective To evaluate the clinical value of ^99mTc-methylene diphosphonic acid (MDP) SPECT/CT fusion imaging and CT scanning in diagnosis of infiltrated mandible by gingival carcinoma. Methods Infiltrated mandible was analyzed in 18 cases of gingival carcinoma by ^99mTc-MDP SPECT/CT fusion images and CT, and compared with pathology findings. Results Eleven of 13 cases with well differentiated squamous cell carcinoma showed positive images, one of 11 cases was false positive images by pathology findings, 10 cases were exhibited infiltrated mandible; 5 cases with moderately differentiated and poorly differentiated squamous cell carcinoma showed positive images, and the result of pathology showed carcinoma cell had infiltrated cavum ossis of mandible. 5 of 18 cases were positive images by CT. Conclusion ^99mTc-MDP SPECT/CT fusion images is an useful method in diagnosis of infiltrated mandible by gingival carcinoma.