An ultrafast front-end ASIC chip has been developed for APD array detectors in X-ray time-resolved experiments.The chip has five channels:four complete channels and one test channel with an analog output.Each complete channel consists of a preamplifier,a voltage discriminator and an open-drain output driver.A prototype chip has been designed and fabricated using 0.13 μm CMOS technology with a chip size of 1.3 mm× 1.9 mm.The electrical characterizations of the circuit demonstrate a very good intrinsic time resolution (rms) on the output pulse leading edge,with the test result better than 30 ps for high input signal charges (＞ 75 fC) and better than 100 ps for low input signal charges (30-75 fC),while keeping a low power consumption of 5 mW per complete channel.