  In this paper, I study the branching ratio of the rare radiative decay $B_s
\to \nu \bar{\nu} \gamma$ in the framework of the Fourth-Generation Standard
Model and the Two-Higgs-Doublet Model. It is shown that this quantity is a very
effective tool for establishing new physics beyond the Standard Model. It is
observed that there is a region in the parameter space in both extensions of
the Standard Model for which the branching ratio show considerable departure
from the Standard Model.
