A light source module including a light guide plate, a light source, and an adhesive material is provided. The light guide plate having a light-coupling region and a light-emitting region includes a light-incident surface, a first and a second surfaces opposite to the first surface, a plurality of first and second microstructures. The light-coupling region is located between the light-incident surface and the light-emitting region. The light-incident surface is connected to the first and the second surfaces. The first microstructures are disposed in the light-emitting region and protrude from the first surface. The second microstructures are disposed in the light-coupling region and protrude from at least one of the first and the second surfaces. A shape of the first microstructures is different from that of the second microstructures. The light source is disposed beside the light-incident surface. The adhesive material is disposed between the light source and the light-incident surface.