Epoxy functionalized siloxanes (EFS) are a novel class of UV curable monomers that can be rapidly photopolymerized to give transparent coatings and composites. Thin films of these materials have been subjected to low Earth orbit exposure to atomic oxygen (AO) aboard the space shuttle. It was found that UV cured samples of all four different EFS monomers exhibited excellent AO resistance both to ambient in-flight conditions as well as exposure at 120 degrees C. Based on SEM, STM, XPS, and weight loss data, it was proposed that AO exposure of these materials efficiently produces a thin layer of SiOx at the surface of the sample. This layer provides a barrier toward further attack by AO.