This manuscript proposed an innovative digital predistortion equalizer using the LMS algorithm. In this article, we used self-made nonlinear circuit boards cascaded with an off-the-shelf RF amplifier to mimic the distorted intermediate frequency (IF) response of a wireless communication system. After applying our proposed algorithm, our prototype demonstrated adaptive equalization within 2 dB bandwidth in the 0.2 - 0.8 Nyquist frequency range (10 - 40 MHz in our case). At this range, the equalizer kept the phase response relatively linear with a group delay less than 10ns. It is foreseeable that our proposed adaptive digital equalizer can be widely used in wireless communication systems.