Oxazolyl fulgide with p-dimethylaniline group (fulgide 1) revealed favorable absorption spectra, high photochromic responses and high thermostabilities in a polystyrene or a poly(methyl methacrylate) film spin-coated on a silica glass, but it suffered from extensive photochemical fatigues while phenyl-substituted oxazolyl fulgide (fulgide 2) revealed much less fatigues. The photochemical fatigues of fulgide 1 could be substantially suppressed by a simple treatment of the spin-coated films to keep air-tight. Similar improvement in the photochemical fatigue resistance was obtained with films of the well-known furylfulgide. Further, thermal stabilities were significantly improved towards heating at 80 degrees C. These effects are ascribable to the effective shielding of the air (molecular oxygen).