The effect of subphase temperature on behaviors and morphologies of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-docosanoyloxymethylspiro[2H-1-benzopyran-2,2'[2H]indol] onto pure water was investigated by measurements of surface pressure-area isotherms and Brewster angle microscopy, respectively. Both depend strongly on the subphase temperature. The isotherms at 30 degreesC show a distinct phase transition at 7.5 mN m(-1), while no such phase transition is observed at 7 degreesC. The morphology changes drastically accompanying the phase transition at 7.5 mN m(-1), at which many large circular domains are formed. Furthermore, we have demonstrated that the morphology changes reversibly accompanying appreciable hysteresis in the isotherms upon continuous compression and expansion cycles. (C) 2003 Elsevier Science B.V. All rights reserved.