Definite clathrate crystals of deoxycholic acid and its amide and alcohol derivatives as host molecules withN-salicylideneaniline as a guest molecule were prepared to investigate their photochromic properties. The photocoloration study was done by irradiating the crystal powder with 365 nm light; the thermal fading reaction of the photocolored species was followed by reflectance spectrophotometry at 303 K. From the sharp difference in the first-order rate constants of the thermal bleaching of the photochromes, it was found that the thermal unimolecular motion of photo-colored species was strongly influenced by the neighboring environments in the crystal state.