A frame structure for backlight modules is provided herein. A backlight module according to the present invention mainly contains a frame structure, a reflection plate, a light guide plate, optical films, and a light source unit. The frame structure contains a plate member and a frame member. There are a number of hook elements and clasp elements configured at corresponding locations along the edges of the plate member and the frame member respectively. Also along the edges of the plate member and frame member, there are a number of grooves and stopping blades configured at corresponding locations on the plate member and frame member respectively. When the frame member is joined to the plate member, their corresponding clasp elements and hook elements would interact to fixedly join together, and the stopping blades would stick into the corresponding grooves to prevent the frame member from deformation and escape under heavy pressure or strong impact.