This paper presents a planar compact microstrip interdigital-coupled notch-band ultra-wideband (UWB) bandpass filter (BPF). The proposed five high-impedance interdigital lines are employed to not only realize strong coupling as feed lines, but also create a controllable notched band in the UWB passband. A prototype of the proposed notch-band UWB BPF has been designed and fabricated. The measured results illustrate that the 3 dB fractional bandwidth (FBW) of the filter is 125%, and the insertion loss of the notched band within the UWB passband is 12 dB at 5.8 GHz.