In order to make benchmark validations of the nuclear data for fusion related materials, absolute leakage neutron from various spherical sample piles were measured earlier at OKTAVIAN. A detailed analysis for Si cross-section is presented here. A leakage neutron spectrum from a Si spherical pile of 60-cm diameter was compared with the calculated results obtained using MCNP-4A with different neutron data libraries. For a detailed study, trial calculations were also performed using modified JENDL-3.2 data libraries. It was found that ENDF/B-VI (release 5) gives the best predictions and the three JENDL data files and EFF-2.4 can predict the measured spectra fairly well. The prediction with FENDL-1.0 file differs by a large extent from the measured spectrum. The discrepancy found in the JENDL, EFF and FENDL calculations are likely to be due to the too low discrete inelastic scattering cross section and too large continuum inelastic cross section values of these libraries, respectively.