  We investigate baryogenesis in the $\nu$MSM, which is the Minimal Standard
Model (MSM) extended by three right-handed neutrinos with Majorana masses
smaller than the weak scale. In this model the baryon asymmetry of the universe
(BAU) is generated via flavour oscillation between right-handed neutrinos. We
consider the case when BAU is solely originated from the CP violation in the
mixing matrix of active neutrinos. We perform analytical and numerical
estimations of the yield of BAU, and show how BAU depends on mixing angles and
CP violating phases. It is found that the asymmetry in the inverted hierarchy
for neutrino masses receives a suppression factor of about 4% comparing with
the normal hierarchy case. It is, however, pointed out that, when
$\theta_{13}=0$ and $\theta_{23} = \pi/4$, baryogenesis in the normal hierarchy
becomes ineffective, and hence the inverted hierarchy case becomes significant
to account for the present BAU.
