A new fast, inexpensive and environmentally benign process requiring only UV light and air for the surface treatment (oxidation) of carbon fibers has been developed that represents a substantial improvement over existing methods. In this new method, continuous fibers are subjected to short wavelength ultraviolet (UV) light which produces ozone from the oxygen in air. UV photons can also react with ozone to create monatomic oxygen, a highly reactive chemical species which is available to oxidize the fibers. Additionally, the UV photons can disrupt and change chemical bonds on the fiber surface to create favorable conditions for reaction with ozone and monatomic oxygen. The result of this two-fold process is the rapid oxidation of the fiber surface that is essential to promote favorable interactions with the matrix in polymer composites. An additional benefit of the UV surface treatment is the improvement in fiber tensile strength. Tensile strength of carbon fibers from pitch as well as polyacrylonitrile (PAN) precursor was found to improve by 10-15% after 90 seconds of treatment. The UV treatment has also been successfully applied to synthetic aramid fibers. The single fiber fragmentation test was used to measure the shear adhesion strength of untreated and treated fibers to an epoxy matrix. The results show that the UV treatment is superior to conventional anodic methods of carbon fiber surface treatment. Following UV treatment, the interfacial shear strength of the pitch and PAN carbon fibers were greater than other surface treatment methods. This presentation will discuss the mechanisms on the interaction of energetic photons in the form of UV light with carbonaceous and polymeric fibers. Results from x-ray photoelectron spectroscopy will be presented that quantify the rapid oxygenation of the surface following UV surface treatment. Changes in carbon fiber surface topography resulting from the photo-oxidative treatments will be presented that indicate that the process removes an incoherent layer of surface atoms. The removal of the defective outer layer results in a structurally stronger substrate for the development of greater fiber-matrix bonding. With the concomitant improvement in tensile strength, it is believed that the UV treatment lead to composites having better mechanical strength that those made using current surface treatment methodologies.