Disclosed is a wavelength tunable light source module for wavelength division multiplexing passive optical network systems, which is capable of being realizing at low costs, increasing utility of wavelength resources, and facilitating mass production. The wavelength tunable light source module comprising: a temperature adjustment unit for raising or lowering ambient temperature according to heat generation or heat absorption caused by an electrical signal, a support block attached to the temperature adjustment unit and having a structure for fixing a laser diode, and a TO-can type distributed feedback laser diode mounted on the temperature adjustment unit by the support block and having an operation wavelength varied according to the ambient temperature adjusted by the temperature adjustment unit.