  Observations of protostellar disks indicate the presence of the magnetic
field of thermal (or superthermal) strength. In such a strong magnetic field,
many MHD instabilities responsible for turbulent transport of the angular
momentum are suppressed. We consider the shear-driven instability that can
occur in protostellar disks even if the field is superthermal. This instability
is caused by the combined influence of shear and compressibility in a
magnetized gas and can be an efficient mechanism to generate turbulence in
disks. The typical growth time is of the order of several rotation periods.
