  We examine whether the magnetorotational instability (MRI) can serve as a
mechanism of angular momentum transport in circumplanetary disks. For the MRI
to operate the ionization degree must be sufficiently high and the magnetic
pressure must be sufficiently lower than the gas pressure. We calculate the
spatial distribution of the ionization degree and search for the MRI-active
region where the two criteria are met. We find that there can be thin active
layers at the disk surface depending on the model parameters, however, we find
hardly any region which can sustain well-developed MRI turbulence; when the
magnetic field is enhanced by MRI turbulence at the disk surface layer, a
magnetically dominated atmosphere encroaches on a lower altitude and a region
of well-developed MRI turbulence becomes smaller. We conclude that if there are
no angular momentum transfer mechanisms other than MRI in gravitationally
stable circumplanetary disks, gas is likely to pile up until disks become
gravitationally unstable, and massive disks may survive for a long time.
