Atenolol (At) beta-blocker antihypertensive active ingredient has been investigated for its X-ray diffraction analysis, thermogravimetric analysis (TGA), differential thermal analysis (DTA), IR-absorption spectra and electronic absorption spectra (UV-VIS) before and after exposure to gamma-radiation doses. The results obtained indicated high resistance of the material against gamma-irradiations. The specific gamma-absorbed doses (40 and 60 kGy) induced higher resistance to gamma-irradiation. Finally the mechanism of gamma-radiolysis is putforward and achieved.