Zinc oxide-thin-layer chromatography has been applied to the comparison of adsorptiveforce of aseries of merocyanine dyes to zinc oxide fine crystals. The merocyanine dyes are 3-substituted 5-[(1-ethy1-4-(1H)-quinolylidene)-ethylidene]-rhodanine derivatives, substituents being hydrogen, ethyl, 2-hydroxyethyl, carboxymethyl, 2-sodium sulfoethyl, 2-diethylaminoethyl, phenyl and 4-hydroxyphenyl. It may be considered that the smaller the Rf value is, the stronger the adsorptive force is, hence inverse order of Rf values shows the order of adsorptive force of the dye molecules. The order of the spectral sensitization efficiency of the merocyanine dyes in zinc oxyde-resin electrophotpgraphic layer was found to agree with the inverse order of Rf values of them. The dependency of the sensitization efficiency of merocyanine dyes upon the adsorptive force was ascertained by this technique. Details of the zinc oxyde-thin-layer chromatography technique are described.