The Dirac or Majorana nature of the neutrinos is still unrevealed. Such neutrino type is determined by the relative size of the Dirac and Majorana mass terms. These mass terms may oscillate if they couple to the wave dark matter. We show the oscillation amplitude can be large enough to change the neutrino type between Dirac and Majorana periodically while satisfying the constraints from dark matter physics. The neutrino type oscillation provides the modulation of the lepton number violation processes like neutrinoless double beta decay. The scale of the oscillation amplitude evolves as the energy density of dark matter decreases over cosmic time. It implies that there is an interesting connection between the leptogenesis in the early universe and the neutrino type oscillation in the present time. This talk is based on the recent paper (arXiv:2305.16900) with YeolLin ChoeJo and Hye-Sung Lee.