  In the supersymmetric standard model, the radiative $B$-meson decay $B \to
X_s \gamma$ could receive a large contribution from a new source of
flavor-changing neutral current, which also violates CP invariance. The
CP-conjugate processes then may sizably differ in decay width. If a new
CP-violating phase is not suppressed, this decay rate asymmetry can be
significantly larger than the prediction by the standard model, possibly
detectable at B factories. Such a large asymmetry may be implied by the
measured branching ratio which is consistent with the standard model.
