Under the collaboration between the Japan Atomic Energy Agency (JAEA) and European Commissions’ Joint Research Center (EC-JRC), development of four active neutron-interrogation nondestructive assay methods for nuclear non-proliferation and safeguards are in progress. The techniques under the development are differential die-away analysis, delayed gamma-ray analysis (DGA), neutron resonance transmission analysis, and prompt gamma-ray analysis. Information obtained by each method is used complementarily to characterize a sample. DGA utilizes moderated pulsed neutrons from a D-T neutron generator to induce fission reaction of nuclear materials. Delayed gamma rays from the fission products (FP) are measured to determine the ratios of fissile nuclides (e.g. 235U, and 239,241Pu) in the sample. Experimental studies of the DGA method are in progress. Delayed gamma ray spectra from nuclear materials were successfully observed with the Pulsed Neutron Interrogation Test Assembly (PUNITA) in EC-JRC Ispra. Here we present an overview of the study plan of these DGA experiments along with the latest results.