The neutron source characteristics of the Japan Atomic Energy Research Institute (JAERI)/U.S. Department of Energy collaborative program on fusion neutronics Phase-IIA and -IIB experiments are determined by measuring neutron spectra and various activation rates in the cavity and on the inner surface of the enclosure and the test regions. The analyses are performed by both JAERI and the United States using individual nuclear data and transport codes. The neutron spectra are generally well predicted by both Monte Carlo and Sn calculations in the energy range of 15 MeV to a few kilo-electron-volts, except for energies 10 to 1 MeV. The discrepancies between the measured and the calculated activation rates are within ±10% when recently evaluated nuclear data are used. Through the present investigation, the characteristics of incident neutrons in the test region can be satisfactorily predicted.