A positioning device for connecting a heatsink to a chip set includes a rectangular frame having a through hole in a center thereof, two side plates extending from two opposite sides thereof and each side plate has one hook extending from an inside thereof. Two positioning rods extend from the other two opposite sides of the rectangular frame, and a plurality of flexible rods extend from insides of the rectangular frame. The heatsink extends through the through hole of the rectangular frame and the positioning rods insert through apertures in the heatsink. The hooks are hooked to two sides of the chip set and the flexible rods press on the heatsink.