This study investigates for optimizing thermal treatment conditions for the effective decontamination of cobalt(Co)-contaminated concrete waste. About 21 g of ordinary Portland cement (OPC, Type I), 37 g of dry sand, 5 g of fly ash, and 24 g of aggregates were mixed, cured for 28 days, and used for characterization and thermal treatment. Thermal treatment was conducted at different temperatures between 105 °C and 600 °C. The samples were characterized using SEM, XRD, FTIR, XRF, and XAS. Up to 600 °C, mass loss only occurred for water molecules in the concrete with ~60% volume reduction, suggesting an optimum temperature between 500 °C and 550 °C. During thermal treatment, Co phase changed from Co3O4 to CoO, and among the various chemical solutions, chloric acid exhibits the highest Co decontamination efficiency. The results suggest that a combination of thermal and chemical treatments can enhance Co removal from concrete waste.