A light source module including a light guide plate (LGP) and a light source device is provided. The LGP has a light exiting surface, a light reflecting surface opposite to the light exiting surface and at least one light entering surface connecting the light exiting surface and the light reflecting surface. The LGP has light reflective structures disposed on the light reflecting surface and each including a closed light active region and protrusions disposed in the light active region. The light active region and the light reflecting surface are not coplanar. The protrusions extend outward from the LGP. The light source device is disposed corresponding to the light entering surface. The light source device provides a light entering the LGP from the light entering surface and exiting the LGP from the light exiting surface after the light is redirected by one of the protrusions on the light reflecting surface.