The present invention relates to a liquid cooling system with water quality monitoring, which comprises a first inlet, a first outlet, a heat exchange unit, a sensing unit, and a control unit connected to the sensing unit and a first pump. The heat exchange unit has a heat exchanger connected to the first inlet and the first pump connected to the first outlet and the heat exchanger. The first pump is used to drive a first working liquid after heat exchange in the heat exchanger. The sensing unit senses a pH value of a first working liquid to generate a sense signal. The control unit compares the sense signal with a preset pH range to generate a compared result which is sent to an external interface. By means of the design of the present invention, the pH value of water can be monitored.