Photosensitivity disorder caused by sunlight, including ultraviolet (UV) rays, often occurs in connective tissue diseases such as lupus erythematosus. In addition, UVA (320–400 nM) and UVB (280–320 nM) trigger the progression of skin inflammation in the patients. Therefore, it is crucial to evaluate skin damage under UV exposure using experimental animals to clarify the relationship between connective tissue disease and photosensitivity disorder. In this chapter, our original protocol for evaluating UVA-dependent skin damage, which is known as photoaging via oxidative stress, is described.