For the quality control in determining transuranic nuclides in fallout samples, this work first reported the 237 Np activity concentration in a reference fallout material and further calculated the activity ratios of 237 Np/ 239+240 Pu and 237 Np/ 241 Am, and the atom ratio of 237 Np/ 239 Pu in it. The reference fallout material prepared by the Meteorological Research Institute was collected at 14 stations throughout Japan in 1963-1979. The 237 Np and Pu isotopes ( 239 Pu and 240 Pu) were separated and purified using AG MP-1M anion-exchange resin, quantified using 242 Pu as an isotope dilution tracer, and determined by the SF-ICP-MS. The analytical method was validated by the analysis of 4 sediment reference materials. The activity concentrations of 237 Np, 239 Pu and 240 Pu were (25.9 ± 0.6) × 10 -3 , 4.10 ± 0.01 and 2.89 ± 0.04 Bq/kg, respectively, in the investigated reference fallout material. The activity ratio of 237 Np/ 239+240 Pu (3.7 ± 0.1) × 10 -3 was consistent with the global fallout evaluation value. The 237 Np/ 239 Pu atom ratio of 0.561 ± 0.014 was higher than the average global fallout value of 0.41 ± 0.010, indicating the necessity of establishing regional characteristic global fallout value of 237 Np/ 239 Pu atom ratio for assessment of radioactive contamination. Comparison of the 237 Np/ 239+240 Pu activity ratios between in the reference fallout material and in soils over several decades indicated that 237 Np has stronger migration capability than Pu isotopes in soils because 237 Np was depleted compared to reference fallout material.