The structures and photoreactions of Langmuir and Langmuir-Blodgett (LB) films of an amphiphilic spiropyran, 1', 3'-dihydro-3', 3'-dimethy1-6-nitro-1'-octadecyl-8- (docosanoyloxymethyl) spiro [2H-1-benzopyran-2, 2'- (2H) -indole] were investigated. The Langmuir films of the spiropyran heated isobarically up to 30°C after compression at 13 °C were transferred on solid substrates as continuous LB films. UV irradiation of the LB films gave rise to J-aggregation without any significant morphological changes. This enabled the patterning of the LB films with 5μm lines of J-aggregates using UV irradiation through a photomask. These results are different from those of the LB films fabricated isothermally at 30°C : the LB films consisted of domains with vacant inter-domain regions and large morphological changes accompanied J-aggregation.