Change in properties of Bi 2 Sr 2 CaCu 2 O 8 + x single crystals due to fast neutron irradiation followed by thermal annealing is reported. Critical current density J c and apparent pinning energy U * 0 were obtained with a vibrating sample magnetometer. The J c and U * 0 decreased due to excess irradiation and increased due to thermal annealing after irradiation. For the specimen annealed at 673 K, J c and U * 0 at 20 and 40 K increased as annealing time increased up to about 24 h. On the other hand, for the specimen annealed at 1073 K, they increased up to 1 or 3 h and then decreased. These results indicate a difference in the change of the defect structure due to the thermal annealing.