The contribution is directed to providing accurate simulation and approximation of the Q-factor determined by thermalelasticdamping in complex micro-electromechanical (MEM) resonators. The base model created is presented as asystem of partial differential equations, which describe the elastic and thermal phenomena in the MEM structure. TheFEM calculations were performed by using COMSOL Multiphysics software. The model was verified by comparingnumerically and analytically obtained damped modal properties of a MEM cantilever resonator. The comparison ofcalculated and experimentally obtained resonant frequencies and Q-factor values indicated a good agreement oftendencies of change of the quantities against temperature. Investigation of longitudinal and bending vibration modes in3D of a beam resonators was accomplished by taking into account the layered structure of the resonator and the influenceof the geometry of the clamping zone. Modal properties of rectangle- and ring-shaped bulk-mode MEM resonators wereexamined, too.The research was supported by NATO RTO; projects LTU-AVT-05/1 and LTU-AVT-07/1.