In this article, we describe the design of the substrate integrated waveguide (SIW) millimeter-wave filtering antenna for 5G communication. It comprises a Γ-shaped slot antenna integrated into a SIW resonant cavity and a bandpass filter (BPF) based on a SIW coupled resonant cavity, which are directly cascaded to form a filtering antenna. The BPF is made up of six resonant cavities, with the opening size between the fourth-order resonant cavities adjusted to achieve magnetic coupling between them. This results in the desired bandpass characteristics. The antenna’s radiation is generated by the Γ-shaped slot structure. To verify the proposed structure and design concept, the filtering antenna was manufactured and measured. The simulated and measured results showed good consistency. The −10 dB impedance fraction bandwidth of the antenna is 2% (25.2–25.7 GHz), with a flat gain of 5.9 dBi within the operating range. The proposed filtering antenna has low loss, simple structure, and low cost, and it is easy to integrate with other electromagnetic sensor systems. It is well-suited for the 5G millimeter-wave band and is anticipated to remain compatible with future generations of mobile communication systems.