Axial graded carbon fibers and silicon carbide fibers with sinusoidal electrical resistivity are prepared by continuous pyrolysis of polymer fibers using an elliptic rotating spool. The electrical resistivity of the graded carbon and silicon carbide fibers hereby prepared varies for 1 similar to 2 orders of magnitude along the axial direction. The tensile strength of both fiber-types is in normal range without remarkable weak point. Desired period and range of the electrical resistivity can be facilely controlled by adjusting the shape of the rotating spool and the pyrolysis temperature.