A memory module assembly includes a plurality of memory modules and a heat sink assembly. Each of the memory modules includes at least one heat source. The heat sink assembly includes a heat dissipating plate and a plurality of heat transfer mediums. Each of the heat transfer mediums includes a base attached to the heat dissipating plate, and at least one resilient sheet extending from an end of the base. The base and the resilient sheet define an included angle which is non-right angle so that the resilient sheet can snugly clip to the respective heat source.