The application of room-temperature ionic liquids (RTILs) to the separation of high level radioactive nuclides from waste water demands a comprehensive knowledge of the radiation effects on the RTILs. Herein, we report a systematic study on the influence of γ-irradiation on the phase behavior and fluorescence properties of the widely used hydrophobic room-temperature ionic liquids [C4mim]X, where [C4mim]+ is 1-butyl-3-methylimidazolium and X- is hexafluorophosphate (PF-6) and bis(trifluoromethylsulfonyl)imide (NTf-2), respectively. It was found that the relaxation time of crystallization in the ILs increased during γ-irradiation leading to a delay before crystallization. The irradiated ILs showed an obvious“red edge effect”similar to that in unirradiated ILs. The whole spectrum, however, shifted to a longer wavelength with increasing the dose and the maximum variation was ca 150 nm. Furthermore, the “red edge effect”was unexpectedly observed in an acetonitrile solution of irradiated ILs and the whole spectrum shifted towards a shorter wavelength with increasing the dilution. All the above-mentioned observations relating to the phase behavior and fluorescence properties are attributed to a change in the spatial correlation between cations and anions in the ILs after γ-irradiation.