An apparatus for forming a serration pattern on a light guide plate having a top surface emitting a light, a bottom surface opposite to the top surface, and at least one side surface, arranged between the top surface and the bottom surface, as an incident surface. The apparatus includes a base plate supporting the bottom surface of the light guide plate; a fixing plate facing the top surface of the light guide plate with a predetermined interval; and a serration core transferring the serration pattern onto the at least one side surface of the light guide plate by a thermal pressing process causing a thickness deformation of the light guide plate. Further, the fixing plate induces a changed thickness of the light guide plate to be uniform by limiting a thickness change amount of the light guide plate to the predetermined interval.