Disclosed are an image forming apparatus and a fixing unit control method thereof, the image forming apparatus including an image forming unit, a fixing unit, a power supply to supply operating power to the fixing unit, a temperature sensor to sense a temperature of the fixing unit, a first protection unit to compare the sensed result of the temperature sensor with a first predetermined reference value and to output a signal, a switching unit to turn on/off power supplied to the fixing unit in accordance with the signal output from the first protection unit, a second protection unit to compare the sensed result of the temperature sensor with a second predetermined reference value and to output a signal, and a relay unit to turn on/off the operating power supplied to the fixing unit in accordance with the signal output from the second protection unit.