Aim: The purpose of this study was to evaluate the biomechanical effects of quad zygomatic implant use in four different type alveolar defect of maxilla. Materials and Methods: Three dimensional models of human skull, zygomatic implants, bar attachment and hybrid prosthesis was modeled using SolidWorks Computer-Aided Design (CAD) program. Four different defect locations were modeled on intact model to mimic different alveolar defect scenarios. In all models, four zygomatic implants were placed on maxilla models at the location of first premolar and second premolar tooth, assembly of the modeled parts were completed. The data were processed by ANSYS Workbench software, 150N vertical occlusal and 300N masseteric load were simulated on modeled prosthesis. The Maximum Von Mises Stress in bone/implants and deformations were visualized and comparatively evaluated with color distribution scale. Results: Among five models, the Maxium Von Mises Stress, in bone, was found in the unilateral defected (1/3 defected) maxilla. The maximum deformation was found in the 2/3 defected maxilla model. In the asymmetric defect models, higher stress values were obtained in the intact part of maxilla. In the models with symmetric defect, it was found that the stress was distributed more homogeneously. Conclusion: Cortical bone thickness, defect size and localization are among the factors closely related to the stability and success of the implant.