A liquid cooling device includes a water tank structure having parallel and separated first and second water tanks. The heat dissipation structure is installed between the first and second water tanks and the three are coupled to each other to form a curved cooling water passage. A mounting portion is formed in the gap between the heat dissipation structure and the first and second water tanks in the extension direction of the heat dissipation structure and the first and second water tanks. Both of the pumping structure and the endothermic structure are coupled to the first and second water tanks. The pumping structure and the endothermic structure are installed in at least one mounting portion and the pumping structure drives a working fluid to flow back and forth between the first water tank, the heat dissipation structure and the second water tank in the curved cooling water passage sequentially.