  We study the interplay between coherence and mixedness in meson and neutrino
systems. The dynamics of the meson system is treated using the open quantum
system approach taking into account the decaying nature of the system. Neutrino
dynamics is studied in the context of three flavor oscillations within the
framework of a decoherence model recently used in the context of LSND (Liquid
Scintillator Neutrino Detector) experiment. For meson systems, the decoherence
effect is negligible in the limit of zero CP violation. Interestingly, the
average mixedness increases with time for about one lifetime of these
particles. For neutrino system, in the context of the model considered, the
decoherence effect is maximum for neutrino energy around 30 MeV. Further, the
effect of CP violating phase is found to decrease (increase) the coherence in
the upper $0< \delta < \pi$ (lower $\pi < \delta < 2\pi$) half plane.
