The merocyanine, 1-alkyl-4-(4-hydroxystyryl)pyridinium halide, shows solvatochromism depending on environmental condition such as pH and polarity of the solvent. We synthesized the merocyanine derivative with a disulfide group tethering it on metal surfaces to form a self-assembled monolayer. The adsorption process of the merocyanine derivative was monitored by in situ surface plasmon spectroscopy (SPS). The SPS and X-ray photoelectron spectroscopy independently indicated that the monolayer was densely packed on a gold substrate. To investigate the solvatochromism following the exposures to organic solutions we applied reflection spectroscopy in the UV-vis region. For more detailed discussions on the reflection spectra, theoretical calculations were carried out on the basis of Fresnel formulas. The results indicated that the merocyanine group shows solvatochromism even in the densely packed layer.