Abstract: In the purpose of achieving a high precise energy measurement in in-beam PET system which being used in heavy-ion cancer therapy, an application specific integrated circuit (ASIC) chip has been designed. Each channel in this four-channel chip consist has a pole-zero cancelation circuit, a low-pass filter circuit and a buffer circuit. The ASIC was fabricated in a commercial 350-nm CMOS process with a footprint of 2.6 mm × 1.25 mm and dissipates 6 mW/Ch of static power in 3.3 V power supply. In four classes peaking time (50 ns、100 ns、1 us、2us), an input dynamic about −0.8~+1 V, an integral nonlinearity (INL) less than 0.12%, an energy resolution less than 0.3%, a crosstalk less than 0.32% and a gain error between 4 channels less than 1.01% have been achieved in laboratory test. A relative energy resolution result was obtained with a Na-22 source, a LaBr₃ crystalloid and a PMT, which is precise than amplifier Ortec 572.