Molecular structure andoptical nonlinearity in interleaving hemicyanine/arachidic acid or cadmium arachidatemultilayers, and Z-type pure hemicyanine multilayers were investigated as a function ofthe temperature by means of second harmonic generation (SHG) and linear absorption. TheSHG intensity shows a maximum at about 45℃ in the multilayers. An inflection was observed in the temperaturedependence of SHG intensity in the interleaving hemicyanine/arachidic acid andhemicyanine/cadmium arachidate multilayers, and was attributed to melting of arachidicacid or cadmium arachidate. The absorption spectra show that the molecules in themultilayers formed H-aggregates which could be dissociated by heating.