Collagen is an abundant extracellular matrix protein that is widely used in the biomaterial, food, and medical fields. Most extracted collagen is soluble in acids and assembles into fibrils under neutral pH conditions. In order to study the effect of UV irradiation on the stability of collagen with consideration of hydratation and fibrillogenesis, UV irradiation of collagen under acid and neutral pH conditions was investigated using electrophoresis, turbidity analysis, and Fourier transform infrared spectroscopy. The relationship between the collagen structure and sensitivity to UV radiation was assessed by studying the effect of UV on collagen under different pH conditions. Results showed that structural changes in collagen caused by UV depend on the degree of hydratation. Soluble collagen completely loses fibrillogeneic ability after exposure to UV for 40 min. Fibrillogenesis of collagen can relieve the UV effect to some degree.