Microstructure and its effect on mechanical behavior of ultrafine interconnects have been studied in this paper using a modeling approach. The microstructure from the processes of solidification, spinodal decomposition, and grain growth in ultrafine interconnects has highlighted its importance. The size, geometry and composition of interconnects as well as the elastic energy can influence microstructure and thus the mechanical behavior. Quantification of microstructure in ultrafine interconnects is a necessary step to establish the linkage between microstructure and reliability.