The residual mechanical properties of epoxy-organoclay nanocomposites after moisture and UV exposure have been evaluated. The flexural modulus decreased after moisture saturation, with much less extent for the nanocomposite than the neat epoxy. The tensile failure strain was significantly reduced with UV exposure time due to the embrittlement effect, and the addition of organoclay mitigated the failure strain reduction. The elastic modulus varied little with UV exposure time regardless of organoclay, because the modulus was determined by the core material which was unaffected by UV exposure. The microhardness and the modulus of the surface material determined from nanoindentation tests increased after UV exposure, with less extent in the nanocomposite than the neat epoxy due to the thinner embrittled top layer for the nanocomposite. All these observations confirmed the beneficial effects of organoclay in improving the barrier characteristics against UV exposure.