OKTAVIAN I was built at Osaka University and has been operated since 1981 as an intense deuterium-tritium (D-T) neutron source at 1.5-ns pulses of 103 D-T neutron/pulse or as a continuous neutron source of 3 × 1012 D-T neutron/s at maximum. This national facility has been devoted mainly to studies on fusion neutron-related subjects by university researchers nationwide and has also served for international collaborations. Annual operating time is usually >1000 h for neutron supply with no special maintenance difficulties. OKTAVIAN consists of a high-current deuteron beam accelerator with some special provisions for maintaining a high D+ atomic ratio for D-T neutron production, highly effective water-cooled rotating solid Ti-T targets for continuous neutron supply, and a nanosecond intense pulse beam supply system with a small air-cooled solid Ti-T target. Special care has been taken to prevent the spread of tritium contamination in- and outside of the facility. Many fusion neutronics experiments have been carried out for the fundamental study of D-T fusion neutron transport characteristics. They have served to improve the evaluated nuclear data files and to test the calculational methods for fusion reactor design, e.g., a series of double-differential cross-section measurements of fusion material by pulsed operation and tritium breeding ratio measurements using a 120-cm natural lithium metal sphere by pulsed or continuous beam operation. OKTAVIAN has been also used for neutron irradiation using continuous D-T neutrons. Several D-T neutron damage experiments have been performed for optical and electronic instruments and components for fusion engineering. The OKTAVIAN-II project, which proposes to supply ∼20 times more intense D-T neutrons than the present facility, is under investigation. Design studies have been carried out, and a series of bench-test experiments is in preparation.