A substrate integrated cavity (SIC)-backed filtering slot antenna with a stacked patch is proposed to enhance the frequency selectivity. The antenna is composed of a slot radiator backed by a SIC, a stacked patch, and a microstrip feed line. Two parallel slots are cut onto the top broad wall of the SIC which is excited by a microstrip line through a non-resonant short slot on the center of bottom broad wall. The stacked patch is positioned right above the SIC supported by a piece of substrate slab for gain enhancement. Compared with the traditional SIC-backed slot antenna, the proposed antenna achieves higher frequency selectivity as well as enhanced bandwidth and gain. The field distribution and parametric study are conducted to exhibit the operating mechanism of the antenna more clearly. Compared with the conventional SIC-backed slot antenna, the antenna prototype operating at 10 GHz, as example, achieves wider 10-dB impedance matching bandwidth of 8.67 %, higher gain of 7.2 dBi, better frequency selectivity of 0.9/0.45 at the lower and upper edges of the operation band, and lower maximum cross-polarization levels of -23/-22 dB in E- and H-planes within the 3-dB beam range, respectively.