Seven tetracycline classes of antibiotics were treated using ultraviolet (UV) and UV/H2O2 oxidation. Two different UV lamps were used for the UV and UV/H2O2 oxidation. The performance of the UV oxidation was different depending on the lamp type. The medium pressure lamp showed better performance than the low pressure lamp. Combining the low pressure lamp with hydrogen peroxide (H2O2) improved the removal performance substantially. The by-products formation of tetracycline by UV and UV/H2O2 were investigated. The protonated form ([1 + H]+) of tetracycline was m/z 445, reacted to yield almost exclusively two oxidation by-products by UV and UV/H2O2 oxidation. Their protonated forms of by-products were m/z 461 and m/z 477. The structures of tetracycline’s by-products in UV and UV/H2O2 system were similar.