  In the case of two generation neutrinos, the energy-scale dependence of the
lepton-flavor mixing matrix with Majorana phase can be governed by only one
parameter r, which is the ratio between the diagonal elements of neutrino mass
matrix. By using this parameter r, we derive the analytic solutions to the
renormalization group equations of the physical parameters, which are the
mixing angle, Majorana phase, and the ratio of the mass-squared difference to
the mass squared of the heaviest neutrino. The energy-scale dependence of the
Majorana phase is clarified by using these analytic solutions. The instability
of the Majorana phase causes in the same parameter region in which the mixing
angle is unstable against quantum corrections.
