The present work investigated the synergetic effect of varying reinforcement sizes (12 μm (coarse), 1 μm (fine), 45 nm (nano)) and cryorolling on aging behavior and mechanical properties of bulk ultrafine grained (UFG) AA6063/4 wt%SiC composites produced via a hybrid route of stir casting and cryorolling. Aging of UFG composites was carried out at different temperatures in the range of 100 °C–175 °C. The results showed that decrease in SiC particle size accelerated the age hardening kinetics and the maximum age hardening effect was observed at 150 °C. The enhancement in age hardening kinetics is attributed to the presence of high dislocation density due to the (i) difference in coefficient of thermal expansion between SiC particles and matrix alloy and (ii) statistically stored dislocation during deformation. Also, the precipitation behavior in UFG composites is established and the microstructural characterization showed the accelerated precipitation kinetics in UFG nano composite. The enhanced age hardening kinetics ultimately improved the strength of the UFG composites compared to UFG base alloy. Among the UFG composites, UFG nano composite showed highest age hardening effect. The overall increase in strength in UFG nano composite is due to the dominant effect of precipitation, dislocation, and grain boundary strengthening mechanisms. © 2019