The rapid oxidation of polyester/cellulosic fiber blend (1:2, 1:1, and 2:1) and of 100 percent polyester, cotton, and viscose rayon in air was studied and characterized by differential thermal analysis (DTA) and scanning electron microscopy (SEM). The study focuses on the nature of the exotherm that occurs following melting of the polyester component in polyester-rich fiber blends and is attributed to oxidation of the polyester component.