A novel optically transparent membrane composed of porphyrin-clay mineral complexes was developed. Reversible solvatochromism behavior of the membrane seas successfully observed, due to an orientation change of porphyrin in the clay interlayer space. The lambda(max) value of porphyrin seas 423 nm in acetone, while it was 464 nm in hexane. The color of the membrane changed from pink to green through to brown, when Sri porphyrin was used. The mechanism for solvatochromism in the present system is very unique compared to those for conventionally reported materials.