In this study, carbon-based materials prepared using an isoperibol oxygen bomb calorimeter of varying oxygen pressure were added to water to form carbon-based suspensions (CBSs). The thermal conductivity, viscosity, density, and contact angle of CBSs were measured by appropriate instruments to understand the fundamental characteristics of CBSs. A differential scanning calorimeter (DSC) was used to measure and analyze the phase-change characteristics of CBSs to evaluate the feasibility of employing CBSs as phase-change materials (PCMs) in ice-storage air-conditioning systems. The experimental results revealed that the thermal conductivity, viscosity, and density of CBSs did not significantly change but a significant reduction in the contact angle of sample's droplets occurred compared with that of water. The CBS of S5 had the lowest melting temperature and subcooling degree (SD) and highest freezing temperature in the DSC experiments; thus, S5 was determined to be the most suitable CBS for use as a PCM in this study.