A dual-passband filter with a notch is proposed. The transmission characteristics of the filter are also analyzed using the odd-even mode theory. The filter is composed of an inverted π resonator, a T-resonator, and an input and output parallel feeder. A step impedance (SIR) is loaded on the branches of the inverted π resonator to suppress the second harmonic of the first passband. Through the overall simulation of the filter and the optimization of its notch frequency and depth, the final notch is located at 1.8 and 6.7 GHz, and the depth can reach less than-19 dB. Finally, the dual-passband filter was processed and tested. The two passbands are 1.44-2.4 and 5.4-7.4 GHz. The insertion loss in the passband is -1.16 and -1.6 dB, and the maximum isolation between the passbands is 50 dB. The measured results agreed well with the simulated results, thus verifying the feasibility of the structure and design method proposed in this study.