To obtain a highly nuclear‐spin vector polarized negative deuterium ion beam, a dual optically pumped polarized negative deuterium ion source has been developed at KEK. It is possible to select a pure nuclear‐spin state with this scheme, and a negative deuterium ion beam with 100% nuclear‐spin vector polarization can be produced in principle. Thus far, we have obtained about 70% of the nuclear‐spin vector polarized negative deuterium ion beam. This result may open up new possibilities for the optically pumped polarized ion source. ©1996 American Institute of Physics.