Conventional parameters derived from the magnetoresistance data have been proposed for the characterization of carbon materials; average transverse magnetoresistance of crystallites (Δρ/ρ) cr for the graphitization degree, and anisotropy factors A1 and A2 for the preferred orientation along the virtual axis of extrusion and in the plane normal to it, respectively. The formulation of these parameters is based on an assumption that the field dependence of magnetoresistance can be ex-pressed by the quadratic law in an approximation. A laboratory-made petroleum coke and a gilsonite coke, whose magnetoresistances seem to be not much deviated from this assumption at 77K, were practically examined; the results show that (Δρ/ρ) cr has a correlation with lattice constant c0 determined by X-ray diffraction as another measure of graphitization degree, and A1 and A2 express well preferred orientation of the samples investigated.