The radiation stability of the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was investigated after ⁶⁰Co γ irradiation at doses up to 600 kGy. Thermal and spectroscopic analysis revealed the formation of a small quantity of radiolytic products and an evident change in the physicochemical properties of the ionic liquid. The presence of anionic FeCl₄⁻ (up to 5 mol%), as measured by UV-vis absorption, differential scanning calorimetry, and Raman spectroscopy, significantly improved the radiation resistance of [Bmim]Cl. The increased resistance may be due to the capture of a solvated electron (e_solv⁻) by FeCl₄⁻ to form FeCl₄²⁻ and results in the radiation protection of the organic cation. The radiation yield of the reductive species (Fe(II)) was estimated to be 0.217 ± 0.010 µmol/J (2.09 ± 0.10/100 eV), which is considered close to the radiation yield of the solvated electrons of [Bmim]Cl.