Interfering signals from various sources may cause a severe performance degradation to GPS receivers. Therefore, lots of efforts have been dedicated to mitigating such interfering signals. However, most of those efforts focused on narrow-band interference cancellation. In this paper, we propose a new anti-jamming scheme by using a wavelet-packet-transform-based (WPT-based) adaptive filter to eliminate chirp-like jammers. We apply a WPT-based de-noising algorithm, which is based on minimax criterion, to generate a reference input to the adaptive filter. Hence, this de-noised signal is able to assist the adaptive filter in generating a better estimation of jamming signals. Simulation results have shown the benefits of the WPT-assisted adaptive filters, which can effectively mitigate a linear chirp with a sweep rate of 2.046 GHz/s and JSR of 45 dB with decomposition level of five. However, a traditional wavelet packet filter can combat the same chirp with the JSR of approximately 35 dB only.