  In this paper, we study the Cabibbo favored non-leptonic $D^0$ decays into
$K^- \pi^+$ decays. First we show that, within the Standard Model, the
corresponding CP asymmetry is strongly suppressed and out of the experimental
range even taking into account the large strong phases coming from final state
Interactions. We show also that although new physics models with extra
sequential generation can enhance the CP asymmetry by few orders of magnitude
however the resulting CP asymmetry is still far from experimental range. The
most sensitive New Physics Models to this CP asymmetry comes from no-manifest
Left-Right models where a CP asymmetry up to 10% can be reached and general two
Higgs models extension of SM where a CP asymmetry of order $10^{-2}$ can be
obtained without being in contradiction with the experimental constraints on
these models.
