Abstract: In this paper, a novel dual-mode dual-band bandpass filter using a quad-mode dual-stub loaded T-type resonator is proposed. The quad-mode resonator is analyzed using odd-/even-mode method. Field distribution of each mode is illustrated, and each mode can be independently controlled. The required extra quality factor (Q_e) can be realized by determining the proper feed-lines parameters, and detail analysis is provided to adjust bandwidth of filter passbands. Then the cause of the zero point of the filter transmission is analyzed get the rule of the zero point change is got for adjusting the zero position and improving the selectivity of the filter. defected ground structure (DGS), etched on the bottom metal surface of the filter, working as a non-resonant node (NRN) and proving source-to-load coupling, are utilized to introduce extra transmission zero to improve the passband selectivity without increasing filter volume. The filter was designed and fabricated, and the simulated results are in accordance with the measured results.