  We consider the effect of Planck scale operators on neutrino mixing. We
assume that GUT scale operators give rise to degenerate neutrino masses with
bimaximal mixing. Quantum gravity (Planck scale) effects lead to an effective
SU(2)L*U(1) invariant dimension-5 Lagrangian involving neutrino and Higgs
fields. This gives rise to additional terms in the neutrino mass matrix on
electroweak symmetry breaking. These additional terms can be considered as a
perturbation to the GUT scale bi-maximal neutrino mass matrix. We assume that
the gravitational interaction is flavour blind and compute the deviations of
the three neutrino mixing angles due to the Planck scale effects. We find that
the changes in theta13, and theta23 are very small but the change in solar
mixing angle theta12 can be as large as 3.5 degrees.
