The ARIES study investigates the potential of tokamaks as fusion power reactors and focuses on improving the economic and safety features of fusion by integrating the environmental constraints into the design from the beginning. The ARIES-II and ARIES-IV designs incorporate advanced physics and technologies that would be available over the next 5–20 years. The two designs have the same plasma physics but different fusion-power-core designs.1 ARIES-II uses liquid Li as a coolant/breeder with V alloy structure while ARIES-IV employs solid breeder with He coolant and SiC/SiC composite structure. Low activation materials were utilized in the design to reduce the radioactive inventory. A variety of blanket/shield options was examined for both designs and the relative merits of the various materials as a function of blanket/shield thickness were demonstrated. The lifetime of the structural components was determined based on the radiation-induced damage in V and SiC. In this paper, a comparison between the two designs based on detailed neutronics analysis is presented.