Objective: The effects of chin cup therapy on the mandible in Class III malocclusions have been investigated extensively via cephalometric analyses. However, the actual sites of mandibular skeletal change are not detectable with conventional cephalometric analysis. It is important to elucidate the association between remodeling of the mandible with the mechanical stress applied with chin cup therapy. Method and materials: In this study, the geometric morphometric changes in the mandible from chin cup force and/or growth were investigated using strain tensor analysis. Results: This geometric morphometric analysis reveals that mandibular deformation arises partly due to a size change and partly due to a shape change. The direction and magnitude of principal vectors of the strain tensors may provide more information about this deformation. Conclusion: Strain tensor analysis may show the degree of transformation within the mandibular geometric configuration due to treatment effects and/or growth changes as seen on lateral cephalometric radiographs.