Abstract: A heatsink plate assembly includes a plurality of heatsink plates laminating each other. Each of the heatsink plates has a first side formed with at least one locking tenon and a second side formed with at least one locking mortise. Thus, the heatsink plates are laminated to have a determined width required by the heatsink plate assembly, so that the width of the heatsink plate assembly is increased according to the user's requirement without being limited to the width of the extruding machine, thereby facilitating fabrication of the heatsink plate assembly. In addition, each of the heatsink plates is made at a time without needing multiple working procedures, so that each of the heatsink plates is produced easily and rapidly, thereby decreasing costs of fabrication.