A fail-safe coolant control valve, comprising: a valve housing provided on an outer surface thereof with at least two ports (10a, 15), the valve housing having therein an internal space communicating with the ports (10a, 15); a valve member rotatably installed in the internal space of the valve housing; an actuator rotating the valve member; and a fail-safe unit (50, 60) rotating the valve member depending on a temperature of a coolant in the valve housing when a failure occurs, wherein the fail-safe unit (50, 60) comprises: a thermostat including a wax contracting or expanding depending on the temperature of coolant drawn into the internal space of the valve housing, and a temperature responding cylinder linearly and vertically moved upward or downward by the contraction or expansion of the wax; and a rotating conversion part integrally formed on a portion of the valve member, the rotating conversion part converting the upward or downward linear movement of the temperature responding cylinder into rotation of the valve member; characterized in that: the rotating conversion part has an inclined surface capable of making contact with a lower end of the temperature responding cylinder when the temperature responding cylinder is linearly moved by the expansion of the wax, the inclined surface including a top dead point and a bottom dead point disposed below the top dead point, and as the lower end of the temperature responding cylinder linearly moves along the inclined surface between the top dead point and the bottom dead point, the valve member is rotated around a vertical axis. a valve housing provided on an outer surface thereof with at least two ports (10a, 15), the valve housing having therein an internal space communicating with the ports (10a, 15); a valve member rotatably installed in the internal space of the valve housing; an actuator rotating the valve member; and a fail-safe unit (50, 60) rotating the valve member depending on a temperature of a coolant in the valve housing when a failure occurs, wherein the fail-safe unit (50, 60) comprises: a thermostat including a wax contracting or expanding depending on the temperature of coolant drawn into the internal space of the valve housing, and a temperature responding cylinder linearly and vertically moved upward or downward by the contraction or expansion of the wax; and a rotating conversion part integrally formed on a portion of the valve member, the rotating conversion part converting the upward or downward linear movement of the temperature responding cylinder into rotation of the valve member; a thermostat including a wax contracting or expanding depending on the temperature of coolant drawn into the internal space of the valve housing, and a temperature responding cylinder linearly and vertically moved upward or downward by the contraction or expansion of the wax; and a rotating conversion part integrally formed on a portion of the valve member, the rotating conversion part converting the upward or downward linear movement of the temperature responding cylinder into rotation of the valve member; the rotating conversion part has an inclined surface capable of making contact with a lower end of the temperature responding cylinder when the temperature responding cylinder is linearly moved by the expansion of the wax, the inclined surface including a top dead point and a bottom dead point disposed below the top dead point, and as the lower end of the temperature responding cylinder linearly moves along the inclined surface between the top dead point and the bottom dead point, the valve member is rotated around a vertical axis.