An orthogonal frequency division multiplexing (OFDM) signal transmission apparatus and a method thereof are disclosed. The OFDM signal transmission apparatus includes an inverse Fourier transform (IFT) unit for transforming a frequency domain OFDM signal to a time domain OFDM signal according to one of transmission modes of 4K, 16K, and 32K; a guard interval inserting unit for inserting a guard interval into the transformed time domain OFDM signal according to a predetermined guard interval inserting rate; and a transmitting unit for transmitting the OFDM signal having the guard interval. Therefore, the data transmission rate is enhanced.