This letter presents a compact multisection sharp-rejection microstrip low-pass filter. Each section is consisted of a microstrip line section and an interdigital capacitor. The analysis for optimizing the attenuation poles by adjusting the finger number, and the width and length of the microstrip line section is presented. The cascaded four-section low-pass filter has a return loss of better than 17 dB and an insertion loss of less than 0.7 dB from dc to 1.6 GHz. The rejection is better than 20 dB from 2.1 to 7.5 GHz.