In this letter, a pin-loaded triple-mode square patch resonator is proposed for bandpass filter (BPF) design. By loading short-circuited pins underneath the patch, the patch resonator not only enables DC-blocking, but also brings out one additional resonant mode, thus a triple-mode patch resonator can be formed up under operation with a pair of degenerate modes. According to the field distributions, these three resonant modes can be tuned by virtue of loaded slots and pins, while these two degenerate modes can be properly split by offset-positioning the two sets of pins. In final, a pin-loaded triple-mode patch BPF is designed, fabricated and measured to validate the predicted results.