A digital alias cancellation technique is proposed in this paper, tailored for the filtering-by-aliasing (FA) receivers. While FA receivers, by using periodically time-varying circuits, achieve sharp analog FIR filtering, due to the sampling nature of it, blockers will be strongly suppressed but then alias in band, which cannot be removed thereafter. The proposed technique cancels the blocker aliases after the sampling operation. Experiments using measured data and MATLAB algorithms show that the stopband rejection within the band of interest can be effectively improved by ~14 dB using the proposed technique.