The radon absorption performance was determined and compared for different types of carbonized boards to establish effective carbonized boards. Moreover, the absorption mechanism of carbonized boards was investigated by specific surface area and pore size in each of the carbonized boards. The radon absorption performance was ranked in the following order: ash (87%), medium-density fiberboard (MDF, 83%), oriented strand board (OSB, 82%), particleboard (PB, 77%), and plywood (PW, 67%). The correlation between radon absorption capacity and surface area or pore volume showed that a higher surface area or pore volume had higher radon absorption performance. However, the highest surface area and pore volume was detected on carbonized MDF, which had a radon absorption performance that was 5% less than carbonized ash board. Therefore, the surface area and pore volume as well as other factors affected the absorption performance.