Langmuir-Blodgett (LB) films of a surfactant squarylium were prepared to investigate formation of H aggregates, which are characterized by blue-shifted sharp absorption bands. The LB films showed an aging effect in room temperature, and annealing was effective to promote H-aggregate formation. Photovoltaic cells of an A1/LB film/Ag structure were also fabricated to investigate the effect of H-aggregate formation for photoelectric conversion. Unlike the case in J-aggregate LB films, action spectra of the photocurrent in the cells were similar to the absorption spectra of the H-aggregate LB films, that is, the H bands can effectively contribute to the photocurrent. The aggregate formation seems to influence the nonradiative decay of excited dyes on metals by coupling with surface plasmon polaritons, which affects the efficiency of photoelectric conversion.