A 25Gb/s energy efficient limiting amplifier (LA) with active feedback is presented. To obtain high energy efficiency, the inverter-based amplifier is employed, and the use of interleaving feedback in the four stages enhances the bandwidth of LA core while maintaining a flat frequency response within the -3dB bandwidth. Fabricated in SMIC 55nm CMOS technology, the measurement results demonstrate that the proposed LA achieves a bandwidth of 18.5GHz with a gain of 36.8dB, and consumes only 17.3mW at 1.5V supply voltage, corresponding to an energy efficiency of 0.69pJ/bit at 25Gb/s operation. Due to the absence of passive inductors and capacitors as well as compact structure, the LA core area is only 0.0008mm 2 .