A light guide module and a light source module are provided. The light guide module includes a light guide plate (LGP) and a first reflective component. The LGP includes a plate body and first microstructures. The plate body has a first light incident surface, a first side surface and a first surface connected thereto. The first microstructures are located on the first surface, and each of the first microstructures has a first optical surface facing the first side surface and the first microstructures are arranged in a first microstructure pattern. The first reflective component is located beside the first side surface, wherein the first microstructures are adapted to cause a light beam reflected by the first reflective component to present a first pattern through the first optical surfaces.