Purpose: The aim of the study was to determine the color and surface chemistry changes of two fiber-reinforced composites and one “advanced composite” as a function of an accelerated aging process by light exposure and water spray. Materials and Methods: Three composites (Artglass, Targis, and Conquest Sculpture) were assessed for color evaluation in three different shades and with XPS analysis. Four specimens of each shade were analyzed with the UV/VIS/NIR Spectrophotometer in reflectance to determine the baseline color for the CIE L*a*b* system. XPS spectra were obtained from three specimens for each material group. All sample disks were artificially aged in a weathering machine and exposed to water spray and a controlled irradiance xenon arc of 0.55 W/m2/nm measured at 340 nm for a total exposure time of 122 hours. L*a*b* and XPS analyses were repeated after the aging process for all specimens. Results: Artglass had “just perceptible,” changes, with
E* between 1.8 and 2.7, while Conquest Sculpture showed, in all shades, “visually perceptible” changes from
E* 5 to 9. Targis had just perceptible as well as visually perceptible changes after aging. All materials showed decreased Ba and Si on the aged samples, while carbon increased. Conclusion: All materials tested underwent a surface change after the aging process. Artglass and Targis changed minimally into whitish/reddish and yellowish appearances, respectively. An organic-rich surface was produced by a combination of washout of filler particles and rearrangement of polymer molecules through diffusion. Int J Prosthodont 2003;16:355–361.