A method of forming a multi-layered thin film uses photolysis chemical vapor deposition (PCVD). In the method, a substrate for a process of forming the multi-layered thin film is prepared. At least two source gases are supplied to the substrate. Reaction lights having particular wavelengths are prepared, which are absorbed by each of the source gases, are prepared. The reaction lights having particular wavelengths are alternatingly emitted on the substrate to a form a predetermined multi-layered thin film. A photolysis chemical vapor deposition (PCVD) reactor is disclosed, having a chamber with a substrate support, a gas supply system for supplying a plurality of source gases to the substrate in the chamber, and a light supply system mounted at one side of the chamber. The light supply system selectively emits one of the plurality of reaction lights having different wavelengths on the substrate.