A liquid cooling device (10) includes a heat sink (12), a panel (14) distant from the heat sink, a heat transfer member includes a heat exchanger (22) thermally engaging with the heat sink and at least one heat pipe (24), a duct (16) connecting with the panel, a flexible tube (18) connected to the duct and the heat exchanger. Therefore, the panel, the duct, the flexible tube and the heat exchanger cooperatively form a hermetical liquid container filled with liquid therein. The at least one heat pipe is extended in the liquid container and submerged in the liquid to transfer heat from one place near to the heat sink to another place in the panel.