A diffuser used in a backlight module including a plurality of light sources is disclosed. The diffuser according to the present invention makes a uniform light output. The diffuser includes a transparent substrate and a plurality of optical structures. The transparent substrate has an entrance surface and an exit surface. The plurality of optical structures is disposed on the exit surface, each optical structure is dented from the exit surface to the interior of the transparent substrate and forms a refractive convex within the transparent substrate, and each refractive convex corresponds to one of the plurality of the light sources. The maximum value of the included angle between the tangent to the refractive convex edge and the normal to the exit surface is smaller than 30 degrees, such that an incident light ray from the light sources refracts and deviates from the normal to the refractive convex through the refractive convex.