Abstract: A real-time α/γ pulse shape discriminator based on CsI(Tl) scintillator was developed. The rise-time method was adopted as the inserted algorithm. The real-time discriminator consists of a high-speed ADC and a high-property PFGA. In this paper, the design scheme and the discrimination algorithm of the system were introduced. The real-time system was tested with a ⁶⁰Co γ source and a ²⁴¹Am α source. The results show that the size of the designed real-time system is small. The discrimination figure of merit is 0.6875. The system can discriminate α and γ events in real time and its throughput of events is up to 2.5×10⁵ s^-1.