In order to investigate the defects in n-type 6H-SiC single crystals caused by neutron irradiation, electron spin resonance (ESR) measurement was carried out for neutron irradiated samples during annealing up to 1,400 degreesC. Six centers arising from radiation induced defects were observed in ESR spectra at liquid nitrogen temperature. The angular dependences and isochronal annealing behaviors of these centers are also described. On the basis of the results, we discuss the structural models for these defects.