  A constraint from $b\rightarrow s\gamma$ process to the minimal
supersymmetric standard model is derived in the light stop region where the
coupling between the lighter stop and the $Z^0$ boson vanishes due to the
left-right mixing of the stop states. It is pointed out that although some
region in the parameter space is excluded from this process there remains a
large parameter space where the amplitude of the $b\rightarrow s\gamma$ is
suppressed due to partial cancellation between different diagrams. Stop as
light as 20 GeV is still viable from the $b\rightarrow s\gamma$ constraint.
