  We investigate the effect of the radion on cosmological perturbations in the
brane world. The S^1/Z_2 compactified 5D Anti-de Sitter spacetime bounded by
positive and negative tension branes is considered. The radion is the relative
displacement of the branes in this model. We find two different kinds of the
radion at the linear perturbation order for a cosmological brane. One describes
a "fluctuation" of the brane which does not couple to matter on the brane. The
other describes a "bend" of the brane which couples to the matter. The bend
determines the curvature perturbation on the brane. At large scales, the radion
interacts with anisotopic perturbations in the bulk. By solving the bulk
anisotropic perturbations, large scale metric perturbations and anisotropies of
the Cosmic Microwave Background (CMB) on the positive tension brane are
calculated. We find an interesting fact that the radion contributes to the CMB
anisotropies. The observational consequences of these effects are discussed.
