Successful restoration depends on the mechanical resistance of dental restorative materials. The occlusal forces from masticatory contacts can affect the durability of restorations and cause fractures. Over time, monomers convert to polymers, leading to degradation of the organic matrix, which can interfere with mechanical resistance. This study sought to assess the effect of artificially accelerated aging on the microhardness of five composite resins: Filtek Z250, Charisma, Durafill VS, Filtek Supreme for body, and Filtek Supreme translucent. Ten test specimens were made of each material, using a 6.0 x 2.0 mm teflon matrix. After 24 hours, five test specimens of each material were submitted to the Vickers microhardness test (control group) for 10 seconds at a load of 300 kgf. The other five test specimens remained in the artificially accelerated aging machine for 196 hours and were submitted to the Vickers microhardness test. Filtek Z250 had the highest values and Durafill the lowest, both at 24 hours and after artificially accelerated aging. Artificially accelerated aging increased the microhardness of the composite resins.