A light guide plate locating construction includes a frame containing a mask and light tube with the light guide plate mounted at the open end of the mask; light permeating through one side of the light guide plate to project in the anticipated direction; locating holes being disposed at the top of the opening end of the mask; a retainer being inserted into the hole; the retainer including a locating portion and an interfering portion extending from the locating portion to the open end of the mask to hold against the edge of the light guide plate to protect the tube from being hit by the light guide plate.