A backlight module including a substrate, a light source, a porous optical film, and a wavelength conversion optical layer is provided. The light source is located on the substrate. The porous optical film is disposed over the light source and has a plurality of emission structures, and the porous optical film distributes light generated by the light source to be emitted through the emission structures located at different positions of the porous optical film. The porous optical film has a central region and a peripheral region surrounding the central region, the central region is disposed corresponding to the light source, and an area of the central portion is A. The wavelength conversion optical layer is located between the light source and the porous optical film, and a vertical projection area of the wavelength conversion optical film is B, where 0.49≤A/B≤5.