Reconstruction of mandibular defects after trauma or tumor resection is one of the most challenging problems facing by reconstructive surgeons. Few mandibular defects require not just a fixation of an implant, but the reconstruction of the entire mandible. It includes deformity, trauma, infection, prior radiation exposure neoplasms, and congenital defect. The aim of this study was to design a mandibular prosthesis for a mandibular cancer patient and study its efficacy by stress-strain related mechanical property using finite element analysis (FEA). One normal young male as well as one old male diagnosed as having mandibular cancer were included in the study. In all the two cases, multi-sliced computed tomography (CT) images of mandible were obtained under standard conditions. The image was analysed by Materialise's Interactive Medical Image Control System (MIMICS) software and ANSYS software. After applying suitable mechanical property of the bone, the biting and chewing forces were applied on the specific regions of the bone in the following cases: i) normal mandible; ii) mandible affected with cancer; and iii) reconstructed (implant) mandible. The maximum value of von Mises stress, and strain were measured; also, the vector sum of the displacement was measured. As expectedly, in mandible affected with cancer, the measured maximum values of Von Mises stress (Pa) as well as the vector sum of the displacement were increased by 50.2% and 41.1% respectively, when compared to normal mandible. On the other hand, the total strain was decreased by 71.4% in the mandible with cancer than in normal mandible. In the reconstructed mandible, the measured vector sum of the displacement and the maximum value of the strain were differed by −16.1% and −4.8% respectively, when compared to normal mandible; whereas, the measured maximum value of the von Mises stress was same in both reconstructed as well as normal mandible. Thus, it showed that, the mechanical behaviour of the reconstructed mandible was close to the same of the normal bone.