This report summarizes the basic aspects of an investigation at 2-mm waveband EPR of magnetic, relaxation and dynamics parameters of various low-dimensional solid-state organic semiconductors with mobile paramagnetic impurities. At high-registration frequency, all components of the g-tensor of such paramagnetic centers are determined. Relaxation and diffusion rates of paramagnetic impurities with different mobilities are determined by the method of steady-state saturation of spin packets