At present, 3-dimensional models of all additive manufactured objects (AMOs) are accepted as a solid model for finite element analysis (FEA). FEA of AMOs may not reveal the real results because mechanical properties of default materials in CAD software and newly built AMOs are not equal to each other. This may produce problems especially for the end user due to unexpected failure or wear off. The aim of this study was to compare FEA results of an additive manufactured Ankle Foot Orthosis model under 2 different value sets, namely default material-based mechanical properties and measured mechanical properties. In order to determine the real mechanical properties of the additive manufactured Ankle Foot Orthosis, 3-dimensional printed test specimens with different infill densities were prepared and tested according to the recommended standards. Mechanical test results were then loaded in the CAD software and FEA was performed. This study illustrated that default mechanical properties of existing materials in CAD software produce misleading simulation results for AMOs, ie, real mechanical properties should be used to get more accurate results.