A light guide device and a backlight module. The backlight module comprises a light guide device and a plurality of light sources. The light guide device comprises a housing, comprising a frame around the housing; and a light guide plate, integrated inside the frame and comprising a light-emitting surface on one side of the light guide plate inside the frame and a light-receiving surface on one edge of the light guide plate, wherein a plurality of slots are disposed between the light guide plate and the frame and on other edges different from the edge whereon the light-receiving surface is disposed, and each of a plurality of barriers is disposed on an inner side of the light guide plate while being adjacent to one of the plurality of slots. The barriers are capable of reflecting the light traveling toward the frame back to the backlight module to improve the light efficiency.