Controlling diastereoselectivity is a challenging issue in the Staudinger reaction. The influence of ultraviolet irradiation on the stereoselectivity in the Staudinger reaction has been investigated. The results indicate that ultraviolet irradiation is one of the most important means to regulate the diastereoselectivity of the products in the Staudinger reaction, whatever ketenes were generated from diazomethyl ketones or from substituted acetyl chlorides in the presence of triethylamine. However, the regulation is dependent on the ketene substituents obviously. Ultraviolet irradiation can even reverse the diastereoselectivity for the reactions involving ketenes without strong electron-donating substituents.