The present work had the objective of studying the treatment of effluents containing free cyanide through the system H2O2/UV, and of selecting the best operational conditions for best efficiency of the process. For that, it was employed synthetic solutions of KCN with characteristics of pH and concentration similar to those of a real effluent. The photoreactor employed in the oxidation tests was a cylindrical reactor of annular section, equipped with a concentrical low pressure lamp of 28 W with emission in 254 nm, where the solution was in direct contact with the lamp. This photoreactor was coupled with a cooling system which kept the operation temperature at 25oC. The evaluated variables were initial cyanide concentration in solution, initial pH of the solution, power of radiated UV and molar ratio [H2O2]/[CN-]. For solutions containing an initial concentration of cyanide equal to 100 ppm, it was possible to reach a removal efficiency of 99.9 per cent in 25 minutes, in pH equal to 9.5, with a molar ratio of [H2O2]:[CN-] equal to 3. For effluents containing an initial concentration of cyanide equal to 300 ppm, at the same operational conditions, it was possible to achieve the same removal efficiency in 30 minutes.