Deterioration of aromas of pummelo essential oil (EO) induced by sunlight was compared to those induced by heat and oxygen exposure using the techniques of sensory evaluation and GC-MS analysis. The sunlight-exposed EO was found to possess an oily off-flavor odor, which was significantly different from its counterparts induced by oxygen and heat. The strong oily note of the sunlight-exposed EO was attributed to the existence of linalool oxides and limonene oxides, as well as the lack of neral and geranial, for which UV sunlight was revealed to be the critical contributor causing the chemical reactions for the aroma changes. The results demonstrated that UV sunlight could significantly affect the aroma of the pummelo EO, providing valuable information that will benefit the production and storage of EO-based aromatic products.