A light guide plate structure, for use with a back light module of a liquid crystal display, has a top surface, a bottom surface, a first end portion, a second end portion which is opposite the first end portion, and a plurality of substantially paralleled V-shape grooves formed on the bottom surface and extending from the first end portion to the second end portion. Each of said V-shape grooves comprises a top angle with a continuous variation from the first end portion to the second end portion. The present invention gets rid of the dark areas of an LCD that appear adjacent to one of the end portions in conventional models, thus enhancing the uniformity in its brightness levels.