  In Calabi-Yau superstring models it is found that two large intermediate
energy scales of symmetry breaking can be induced for special types of the
nonrenormalizable interactions. In the models one set of $SO(10)$-singlet,
right-handed neutrino and their mirror chiral superfields is needed. Through
the study of the minimization of the scalarpotential, the conditions for the
presence of two large intermediate scales are obtained. In this scheme a
Majorana-mass possibly amounts to $O(10^{9 \sim 10}\gev)$. This large
Majorana-mass solves the solar neutrino problem and also is compatible with the
cosmological bound for stable light neutrinos.
