A substantial reduction of Substrate Integrated Waveguide (SIW) insertion loss can be achieved through the use of air as dielectric instead of usual dielectric material. However, Air-Filled SIW (AFSIW) circuits exhibit larger footprint compared to their dielectric-filled counterparts. In this letter, a compact multilayer AFSIW bandpass filter is proposed to realize both high performance and small footprint. For demonstration purpose, a Ka-band multilayer 4th order AFSIW bandpass filter has been designed and fabricated. Measured and simulated results are in good agreement. Retro-simulations, taking into account fabrication tolerances, are also presented. Finally, a performance comparison with other multilayer technologies is presented.