Abstract: Plants have evolved the capacity responding to a wide range of environmental signals, one of the most important of which is light. Ultraviolet light and blue light play an important role in the development of plants. The purpose of this article is to review the studies on ultraviolet light and blue light receptors, and the effect of ultraviolet light and blue light on expression of CHS, the gene e ncoding chalcone synthase (CHS) which acts in the first committed step in the flavonoid biosynthesis pathway. The possible components in the signal transduction are introduced as well.