A liquid-cooled heat sink assembly for cooling down an electronic component includes a main body (20) defining a central chamber (21) therein and having a number of fins (22) on an outside thereof, liquid coolant received in the central chamber, a first fan (40) received in the central chamber, and a second fan (60) positioned over the main body and engaged with the first fan. The heat sink assembly couples forced liquid cooling and forced airflow cooling, and need not extra pipes to form a circuit for the liquid coolant. Thus, not only the volume of the heat sink assembly is lessened, but also facilitates matching with electronic components.