A wavelength conversion module and a projection device are provided. The projection device includes an illumination system providing an illumination light, a light valve forming the illumination light into an image light, and a projection lens forming the image light into a projection light. The illumination system includes an excitation light source providing an excitation light, and a wavelength conversion module receiving the excitation light. The wavelength conversion module includes a case and a wavelength conversion layer. The case has a liquid inlet, a liquid outlet, and a cavity connecting the liquid inlet and the liquid outlet for circulation of a cooling liquid. The wavelength conversion layer is located on the case, wherein the relative positions of the wavelength conversion layer and the excitation light remain unchanged. The projection device and the wavelength conversion module have good reliability.