This letter presents a novel miniaturized differential dual‐band bandpass filter (BPF) using a single quad‐mode metal‐loaded dielectric resonator (DR). The differential dual‐band BPF is designed in a single‐cavity configuration with one quad‐mode DR and four feeding probes, featuring compact size. The rectangular DR is directly mounted on the bottom of the metal cavity and covered by a metal plate on the top surface. It allows two pairs of orthogonal modes (LSE10 and LSM10), which can be differentially excited and coupled by introducing proper perturbation for constructing dual‐band differential‐mode frequency response. To validate the proposed idea, a compact differential BPF with good performance using a quad‐mode DR cavity is designed, fabricated, and measured. The simulated and measured results with good agreement are presented.