A light guide plate and a plane light source unit are provided. The light guide plate for a plane light source unit includes a plurality of unit pattern regions each having a plurality of optical patterns on surfaces thereof, wherein one or more unit pattern regions have different sag values (height:lens size) of the optical patterns constituting the unit pattern regions. Unit pattern regions are implemented with segmented optical patterns, which are equal in height, from the outside of the light guide plate to the central part thereof, by adjusting the density and size of microlenses, thereby improving the light uniformity and light efficiency and improving the efficiency of manufacturing processes.