Abstract: In order to solve the problem that the reflected signal may damage the system performance, a miniaturized absorptive low-pass filter with high out-of-band rejection and high out-of-band absorption is proposed. The absorptive behavior is achieved through a high-pass channel and a low-pass channel. The high out-of-band rejection is achieved by stopband rejection raising channel. The filter is simulated and optimized in ADS and HFSS simulation softwares, and is fabricated on the substrate of GaAs. The measured results show that the 3 dB cut-off frequency of the filter is 4 GHz. The minimum in-band insertion loss is 0.88 dB, and it has an excellent characteristic with return loss from DC to 3.5 GHz more than 20 dB, and the stopband return loss more than 10 dB. The stopband rejection is more than 45 dB at 10.5 GHz, and the out-of-band rejection is more than 33 dB from 8 GHz to 30 GHz. The measured results are in good agreement with the simulation results. Furthermore, its dimension is only 1220 μm×650 μm×87.71 μm. Compared with conventional filters by PCB and LTCC technology, the size of this filter is greatly reduced, which accords with the trend of miniaturization in modern RF and microwave systems.