According to a method and apparatus for controlling a voltage of an image forming apparatus, a transferring roll resistance, which indicates the resistance between a transferring roller and a photoconductor drum, is detected by applying a first voltage to the transferring roller. A transferring voltage, which corresponds to the detected transferring roll resistance, is applied to the transferring roller with reference to a transferring table which corresponds to the paper resistance, and a transferring is performed on a printing paper by using a transferring roller to which a transferring voltage is applied.