This study investigated the microhardness and fracture toughness values of five dental indirect resin composites under the effect of thermal cycling by single-edge notched beam method. Highest microhardness and fracture toughness were reached in AP-X and Filtek P60 groups (microhybrid resin composite) (P<0.05). After thermal cycling, significant changes of fracture toughness were found for the tested composites except AP-X. Microdifferences between scanning electron microscope images with and without thermal cycling were observed. It is concluded that irregular-shaped fillers and higher filler content contribute to higher mechanical properties, microhardness, and fracture toughness and result in superior fracture toughness under the effect of thermal cycling.