The present invention provides a light source module for using in a backlight module which includes a frame, a light source and a lid. The frame has two opposite side walls, and each of the side walls includes an inner side surface, a top surface and a cave. The cave has a first opening and a second opening connected with each other on the inner surface and the top surface respectively. Each of the inner surfaces is facing the other side wall, and the top surface intersects the inner surface with an angle. A light source has two opposite ends, and each of ends includes a positioning block. The positioning block engages with the cave through the second opening, and the light source extends along a first direction perpendicular to the inner surface, through the first opening and towards the opposite side wall of the frame. The lid covers the second opening and restricts the positioning block from moving relatively to the cave from the second opening.