Orthogonal frequency division multiplexing (OFDM) is considered to be one of the promising schemes for cognitive radios (CR) systems,due to its flexibility in spectrum shaping.However,the traditional way of spectrum-notching failed to suppress out-of-band leakage enough,resulting in interference with licensed users (LUs).A novel spectrum shaping scheme is proposed in this article,where a precoder with interference suppression sequence (ISS) is for the first time introduced for shaping the spectrum of OFDM signals in OFDM-based CR systems.The precoder matrix together with ISS matrix is obtained by minimizing the power of out-of-band interference,which results in the sufficient interference suppression of OFDM signal to LUs.Analysis and simulation results show that the proposed scheme can significantly suppress the interference power to LUs at a little cost of precoding efficiency.Meanwhile,the peak-to-average-power-ratio (PAPR) is invariable and the bit-error-rate (BER) performance over Rayleigh fading channel is improved.