Abstract: The BC501 scintillator has been widely used as a detector of fast neutron. A technique using pulse rise time separation method for the use of neutron-gamma pulse shape discrimination is reported. In order to search better scintillator of n-γ and energe discrimination, n-γ energe spectra are measured with BC501 scintillators with different size. A pulse rise time separation spectra of n and γ are obtained using AmBe neutron slowed by paraffine upon 0.75 and 1 MeV. In the same condition, γ-spectra are obtained by a ²²Na source, and the energe spectra of neutron are obtained by d-T 14 MeV neutron from accelerator. The n-γ and energe discrimination from the BC501 scintillators with different size is compared. By selecting a scintillator with suitable length and volume, the n-γ and energe discrimination is achieved extremely well.