Electrical properties of n-type SiC single crystals irradiated with reactor neutrons at temperatures below 100K have been investigated by resistivity and Hall effect measurements at room temperature. In the neutron irradiated SiC, the carrier mobility rises with increasing of the initial carrier density. In heavily doped samples, the results of the thermal annealing of the irradiated SiC indicate that the resistivity and the mobility have two annealing stages (350K, 500K) and that the carrier density keeps constant up to 823K. From these facts, it is suggested that the electrical properties of n-type SiC irradiated at low temperature are strongly affected by the existence of donor.