A tunable dual-mode dual-band square cavity substrate integrated waveguide (SIW) bandpass filter is proposed. Metalized via-holes are inserted into the center of the cavity as perturbations to move and control the four resonant modes to create the dual passband filter. The first passband is formed by the perturbed TE 201 and TE 202 modes, while the second passband is formed by the perturbed TE 301 and TE 302 modes. Moreover, moving the perturbed via-holes on the SIW cavity allows the first passband to be tuned separately while the second passband is almost fixed. A dualband filter prototype with frequencies of 17 GHz and 19.36 GHz and three transmission zeros (TZs) has been designed, fabricated, and measured. The measured and simulated results are in good agreement, confirming the proposed dual-band filter design concept.