The radiolytic decomposition of oxytetracycline and effects of inorganic ions were studied. The removal efficiency of oxytetracycline, 30 mg/L, was 99% at the irradiation dose of 0.7 kGy. Chloride, sulfate, nitrite, nitrate and phosphate had effects on oxytetracycline degradation. Especially, nitrite and nitrate showed the significant inhibition effect on the radiolytic degradation of oxytetracycline by an ionizing radiation.