Relationships between morphology and micromechanical deformation processes in various toughened and particle-filled semicrystalline polymers with different types of modifier particles have been investigated by high voltage electron microscopy and scanning electron microscopy using in situ tensile techniques. From the study of phase structure of modifier particles, two morphological standard types are classified : the binary system (homogeneous modifier particles are dispersed in the matrix), and the ternary system (heterogeneous modifier particles are dispersed in the matrix). Taking into account these categories and the phase adhesion between the modifier particles and the matrix, micromechanical deformation processes have been characterized. As initiation sites of plastic deformation the microvoid formation is considered, which plays an important role for the activation of further plastic deformation of matrix material during deformation processes. According to the morphology of modifier particles this microvoid formation is caused by either cavitation in the stretched rubbery shell/inside particles or debonding at the interface between particles and matrix.