Determination of gear resonance frequencies is necessary in the design of light weight aerospace gears. Resonant frequencies and mode shapes calculated are then identified as damaging or non-damaging and compared to the gear's mesh frequencies to determine if gear tooth bending stresses will be amplified in a particular operating speed range. Finite Element Analysis (FEA) is well suited to determining gear resonant frequencies and modes. In order to verify the analysis quickly@ rough gear geometry is fabricated and tested using accelerometers and a calibrated hammer in a modal excitation test. In past efforts@ rough geometry fabricated was a simplified version of the final part minus gear teeth or other features. To reduce the time of fabrication and to increase the accuracy of the prototype part@ modern rapid prototyping manufacturing techniques may hold promise in approaching the realism of the actual part with material properties that are similar to material properties of gear steels. This paper studies gear resonance modal excitation testing of two stage idler spur gear rapid prototyped parts@ using two different rapid prototyping techniques and compares results to the final production part and FEA model. Damaging and non-damaging modes and nomenclature will be reviewed as well as the testing method.