An apparatus and method for orthogonal frequency division multiplexing (OFDM) transmission in a wireless local area network (WLAN) system is disclosed, in which the apparatus for OFDM transmission in the WLAN system includes a signal repetition unit to repeat an encoded signal based on a block unit and output the encoded signal and a repeated signal, an interleaver to interleave the encoded signal and the repeated signal and output an interleaved signal, a modulator to modulate the interleaved signal and output modulated symbols, and a phase rotation unit to phase shift the modulated symbol.