C60 and C70 fullerenes were neutron-bombarded to an integral dose of 3.28×1016 n cm−2. After the neutron treatment the trichloromethane soluble fraction was determined spectrophotometrically and C60 insoluble fraction was found at 3.8% while the insoluble fraction of C70 17.9%. The formation of the CHCl3 insoluble fraction is due to polymerization and incipient amorphization of the neutron-bombarded fullerenes where C70 appears more sensitive to radiation damage than C60. Raman spectroscopy was used for the characterization of the irradiated fullerenes as well as electron spin resonance (ESR) and electronic absorption spectroscopy on solid samples. Differential scanning calorimetry (DSC) to 630°C was employed for the determination of the Wigner energy of the neutron-damaged fullerenes. The results are consistent with a higher level of radiation damage reached by C70 in comparison to C60 at the same neutron dose.