A light guide plate (10) includes a pair of opposite incidence surfaces (101, 103), an emission surface (108) and a bottom surface (109) opposite to the emission surface. A plurality of dots (11) is distributed on the bottom surface, and each dot is shaped as a rectangle or a square with one corner thereof cut away. Thus, a clearance between adjacent dots is relatively small. That is, a distribution of the dots is relatively compact, and this ensures that the light guide plate can provide emission of light beams with good uniformity. Furthermore, adjacent rows of dots are offset, and this offset can avoid bright lines. Thus, the light guide plate can provide improved display quality. Therefore, the light guide plate can be advantageously applied in back light systems of liquid crystal display devices.