  The propagation of neutrinos in a gravitational field is studied. A method of
calculating a covariant quantum-mechanical phase in a curved space-time is
presented. The result is used to calculate gravitational effects on the
neutrino oscillation in the presence of a gravitational field. We restrict our
discussion to the case of the Schwartzschild metric. Specifically, the cases of
the radial propagation and the non-radial propagation are considered. A
possible application to gravitational lensing of neutrinos is also suggested.
