The orientations of cationic porphyrins on a clay surface were found to be successfully controlled by solvent polarity. The orientational change was directly observed with the interface spectrometer equipped with a quartz waveguide system. Tetracationic porphyrins on the clay Surface in water are oriented with the plane of the rings parallel to the silicate layer, while in the case of dicationic porphyrins (cis-type), the porphyrin plane stood Lip against the clay surface on addition of less polar water-miscible solvent.