Pulse height and timing characteristics of CsI(Tl)-Si(PIN)detector have been investigated for γ-rays and fission fragments(FFs). Energy dependence of the scintillation light output has been studied for FFs from a ²⁵²Cf source by degrading their energy in P-10 gas at different pressures. It is seen that the light output for both heavy and light mass groups increases linearly with energy in the interval of 0.2–0.9MeV/A. At a given energy, the light output is more for the heavy mass fragments than for light mass fragments. The time resolution for g-rays was determined to be 134±3 ns using a BaF₂ as start and CsI(Tl)-Si(PIN) as stop detector.