The effects of neutron irradiation on poly crystalline α-alumina were investigated. The specimens were translucent solid cylinders of 99.8% of theoretical density with an average grain size of 25 μm. Fast (> 1 MeV) neutron exposures ranged from 0.6 to 5.2 × 1021 n/cm2 where the thermal-to-fast flux ratio varied from 1.6 to 1.1. Temperatures of the specimens were calculated to range from 300 to 600°C. Grain-boundary separation was observed when the neutron dose (> 1 MeV) was approximately 2.3 × 1021 n/cm2, and it became progressively worse with increasing neutron dose. Extensive fracture was observed in specimens exposed to doses above 3 × 1021 n/cm2 (> 1 MeV), but there was virtually no fracturing of samples exposed to doses less than 2 × 1021 n/cm2. Volume of the specimens increased as the neutron dose increased, but the volume as calculated from the lattice parameters, which increased in specimens exposed to a neutron dose of 0.7 × 1021 n/cm2, decreased slightly with additional radiation. Above 0.7 × 1021 n/cm2, the a parameter remained constant while the c parameter decreased. It is suggested that grain-boundary separation, which causes the fracturing of the specimens, is produced by an anisotropic expansion of the crystals produced by defect agglomerates which are too large to affect the lattice parameter measurements.