Experiments on photo-decomposition of CFC-115 bubbled in an alkaline alcoholic solution were carried out in a photochemical reactor irradiated by a 32 W low-pressure mercury-vapor lamp. It was found that initial decomposition rate of CFC-115 was governed by a chain reaction, and the reaction rate increased with partial pressure of CFC-115, was independent of sodium hydroxide concentration, and proportional to the square root of the light intensity. Based on this, a radical reaction mechanism of initial photo-decomposition is proposed.