AbstractAnalysis of the Karlsruhe neutron transmission experiment has been performed using the three-dimensional Monte Carlo code MCNP version 4B in order to investigate the accuracy of various beryllium nuclear data. The EFF-1 reproduced best with the measured total neutron multiplications among five files. Significant discrepancies between calculated and measured leakage spectra, however, were observed in some energy windows for all beryllium nuclear data, which were due to the difference of the secondary energy and angular distribution of neutrons emitted through the 9Be(n, 2n) reaction among various beryllium nuclear data.