A mixed water control valve for a faucet includes a control unit, two mounting seats and a balance unit. The control unit includes a valve housing, a rotation plate and a control handle. The balance unit includes a fixed sleeve and a pressure regulating sleeve. The pressure regulating sleeve is movable in the fixed sleeve by a pressure differential between the two mounting seats to control the water flow rate of the cold and hot water of the two mounting seats and to regulate the water pressure automatically so as to provide a pressure balance and to stabilize the temperature of the mixed cold and hot water in the valve housing so that the mixed water flowing from the valve housing is kept at a constant temperature.