An apparatus and method of testing a printhead nozzle includes a power supply unit to supply a power to the printhead, a capacitor to stabilize a voltage of the power supply unit so that the power supply unit supplies a constant power to the printhead, a voltage sensing unit to sense a voltage of the capacitor, a nozzle testing unit to test the nozzle using the sensed voltage to detect an abnormal condition of the nozzle, and a control unit to control driving of the power supply unit and the nozzle.