A method for spectrum spreading in an orthogonal frequency division multiplexing (OFDM) system is proposed in this paper, resulting in a spread spectrum OFDM (SS-OFDM) system suitable for ultra-wideband (UWB) applications. By modifying the IFFT module in a conventional OFDM transmitter and interleaving the modulated signal samples within an OFDM symbol, the transmitted signal spectrum is spread greatly to realize spread spectrum communications. This method of spectrum spreading is also compared with that of the multiband OFDM (MB-OFDM) system. The SS-OFDM signal has the characteristics of a white noise, and its power spectrum density is constant within the desired bandwidth. One of the main advantages of the proposed system is that it can be used for UWB communication without the need for frequency hopping. In addition, the transmitted signal bandwidth can be selected flexibly to meet different system requirements.