Sensitivity of aqueous solutions of fungal guanyl specific RNase Th to irradiation with different doses of γ-rays was studied. Enzyme activity, aggregation, amino acid composition, UV-absorption and difference spectra of native and irradiated enzyme were investigated. Inactivation of RNase Th after irradiation occurred with all doses used and alterations in the spectral properties of the enzyme were observed. The reasons of these deviations most likely are changes in the conformation as a result of breaking of hydrogen and disulfide bonds and destroying of one molecule of tyrosine. The data received for the sensitivity of this enzyme to gamma-irradiation could contribute to more detail characterization of this family of proteins