We have studied the effect of the fast neutron irradiation on the critical current properties and the microstructure of Melt-Textured Growth (MTG) YBa 2 Cu 3 O 7−δ with fluences of 2.3 × 1016 n/cm 2, 1.16 × 1017 n/cm 2, and 5.8 × 1017 n/cm 2 respectively. The hysteresis loops have been measured at 77 K and 1.5 K in the applied magnetic fields between −6 T and 6 T. The irreversibility lines H(T*) were also demonstrated. The critical magnetization current density J c is up to 4.7 × 105 A/cm 2 at 77 K in the field of 0.1 T for the irradiated sample with the fluence of 1.16 × 1017 n/cm 2. It is tenfold higher than that of the unirradiated sample. This increase of J c is due to the pinning at irradiation–induced pinning centers. Much higher neutron irradiation with fluence of 5.8 × 1017 n/cm 2 is harmful to the increase of J c value because the orthorhombic structure has been transformed into the tetragonal one. The amorphous state and the cellular structures are also observed in the irradiated MTG sample.