Unsymmetrical carbocyanine dye, containing one nucleus having sensitizing ability, the other one having desensitizing effect was measured for absorption spectrum, polarographic half-wave potential and sensitizing effect for silver halide emulsion. The following results were obtained. 1) The hyper-redox potential of these dyes confirmed to lie near redox potential of silver bromide (0.24 V vs. SCE). 2) For relationship between excitation energy and polarographic half-wave potential, these dyes exist among the range of sensitizing dye and desensitiziug dye. 3) Spectral sensitizing ability of unsymmetrical carbocyanine dye can be estimated as the sum of sensitizing ability of each nuclei-desensitization will be considered as minus sensization-. 4) Few dyes having none of ability to sensitize and to desensitize silver halide may be used as anti-irradiation dye.