This study assessed the histologic and histomorphometric changes of free gingival grafts in a canine model after mechanical expansion. A total of eight epithelialized tissue samples were obtained from the palate of eight Beagle dogs. Samples were cut in half and separated into two groups: the test group, in which a device was used to expand the grafts, and the control group, without expansion. After histologic processing, samples were evaluated by qualitative histology and histomorphometry. Histologic analysis revealed some differences in epithelial cell morphology and keratin layer integrity in the test group compared to the control group. Differences in histomorphometric parameters for the expanded and nonexpanded groups, including the thickness of the keratin layer (15.4 ± 13.4 μm and 32.3 ± 18.1 μm, respectively), thickness of the epithelium (398.0 ± 168.0 μm and 368.4 ± 142.8 μm, respectively), and the area occupied by collagen fibers in the connective tissue (62.0% ± 11.0% and 55.8% ± 7.6%, respectively), were not statistically significant (P < .05). Despite some changes in qualitative histology, free gingival grafts maintained their histomorphometric characteristics after mechanical expansion. These data provide a scientific basis for the use of mechanical expansion as a possible procedure to reduce the morbidity of autogenous grafts because a single soft tissue sample can be expanded before grafting. Int J Periodontics Restorative Dent 2023;43:e89-e97. doi: 10.11607/prd.5752.