We newly synthesized transparent films composed of pH-sensitive spin-crossover complex [Fe-II(diAMsar)] (diAMsar: 1,8-diaminosarcophagine) and an ion-exchange polymer, Nafion, having different colors corresponding to proton concentration. The UV-vis spectroscopic measurements revealed that the films, which were provided under pH 4, 7, and 10 conditions, showed the spin state depending on pH.