In this study, a dual-frequency microstrip bandpass filter with a folded step impedance resonator structure is proposed. The filter is miniaturized by a novel parallel electrical coupling method, and the zero-degree feed structure is introduced to generate transmission zero points to improve the out-of-band suppression performance. The experimental results show that the filter has a compact structure, low loss, and good out-of-band rejection performance. The center frequency of the passband is 2.4 GHz and 5.2 GHz, respectively. The in-band performance is good, and the minimum insertion loss is 0.72 dB and 0.69 dB, respectively.