The radon adsorption ability of four samples of coconut shell-based activated carbons has been investigated by measuring the dynamic adsorption coefficient (DAC) of each activated carbon in a radon room. The findings obtained have shown that DACs are dramatically different even when the surface areas are near. Nitrogen adsorption and X-ray photoelectron spectroscopy analysis are used to study the microstructure of the four samples. The results have shown that micropores with diameters between 0.5 and 0.8 nm play the most important role in radon adsorption on activated carbons. Oxygen on the pore surface influences radon adsorption because of the polarity molecular adsorption on oxygen groups.