The present invention relates to a transmitter in an OFDM system for improving the PAPR, and a method thereof. According to the exemplary embodiment of the present invention, channel encoding is performed in order to correct a data transmission error of a radio channel, a predetermined bit of the channel encoded data is bit-inverted by using a mask bit or a mask bit sequence, and a PAPR of the signal is reduced. Accordingly, reduction of transmission efficiency which has been generated in block coding and DSI methods is not generated when the signal is transmitted because an additional bit is not required.