Electron injection from excited rose bengal into the conduction band of a thin film of $SnO_2$ semiconductor in acetonitrile was investigated in an electrochemical cell, ITO/$SnO_2$/rose bengal, NaI or $I_2$, $NaClO_4$/Pt. It was observed that NaI enhanced the supersensitized photocurrent, followed by the slow reduction, whereas $I_2$ yielded a fast decaying photocurrent. Spectroscopic analyses of the dye solution containing NaI revealed that electron is transferred to the $SnO_2$ electrode from the reduced rose bengal and iodide is responsible for the reduction of the dye in triplet state. However $I_2$ appears to possess neither the reducing ability of the oxidized dye nor the retardation of the dehalogenation of RB.