  The KM3NeT/ORCA sensitivity to atmospheric neutrino oscillation is presented.
The event reconstruction, selection and classification are described. The
sensitivity to determine the neutrino mass ordering was evaluated and found to
be 4.4 $\sigma$ if the true ordering is normal and 2.3 $\sigma$ if inverted,
after three years of data taking. The precision to measure $\Delta m^2_{32}$
and $\theta_{23}$ were also estimated and found to be $85\cdot10^{-6}$ eV$^2$
and $(^{+1.9}_{-3.1})^{\circ}$ for normal neutrino mass ordering and,
$75\cdot10^{-6}$ eV$^2$ and $(^{+2.0}_{-7.0})^{\circ}$ for inverted ordering.
Finally, a unitarity test of the leptonic mixing matrix by measuring the rate
of tau neutrinos is described. Three years of data taking were found to be
sufficient to exclude $\nu_{\tau}$ and $\bar{\nu}_{\tau}$ event rate variations
larger than 20% at 3$\sigma$ level.
