EDF R&D carries out studies for many years in order to improve and quantify the performances of the ultrasonic NDT process implemented on nuclear power plants. The detection and sizing of defects in coarse grained materials is a very challenging issue related to the inspection of critical components of nuclear power plants. Indeed in coarse grained material, the scattering of the ultrasonic wave at grain boundaries is responsible for the high attenuation which highly degrades the detection performances. This unfavorable phenomenon is predominant where the mean grain size is comparable to the wavelength of the control. In this framework, EDF R&D has carried out studies on the simulation of the ultrasonic propagation in complex materials with the finite elements code ATHENA. 2D and 3D finite element modeling approaches of ultrasonic propagation have been implemented, combined with a description of the microstructure of coarse grain materials [1]. The aim of this study is to demonstrate that the integration of a relevant description of the microstructure of macroscopically isotropic grain materials in a numerical simulation is an efficient tool to predict the ultrasonic attenuation in those materials. In addition, the influence of grain morphology, size and orientation on the ultrasonic attenuation coefficient is studied. The simulation results are compared with theoretical models and experimental measurement performed on an isotropic polycrystalline material (coarse grain Ni-based alloy).