Degummed silk from Bombyx mori was dissolved in 9.3M lithium bromide solution. The regenerated silk fibroin films were completely ${alpha}$-randomcoil type as shown by x-ray diffraction and infrared spectroscopy. The structural changes in silk fibroin induced by immersion into methanol and dilute hydrochloric acid and its photo-yellowing effect was studied. The changes of crystallinity were measured by infrared spectrometer. Yellowness index caused by ultraviolet irradiation were observed as a function of the structural change on silk fibroin. On treatment with methanol, ${alpha}$-randomcoil silk film is converted to the ${eta}$-form structure. After the treatment of hydrochloric acid on ${eta}$-form structure in silk induced by immersion into methanol, ${eta}$-form in silk fibroin is partially decreased. Crystallization owing to ${eta}$-form transition reduced the initial yellowness index by ultraviolet irradiation. A little ${eta}$-form structure in silk fibroin increased the initial yellowness in comparison with more ${eta}$-form structure.