Activated carbons were prepared from a carbonized RDF (cRDF) by steam-activation. The cRDF was obtained by carbonizing the RDF at 773 K. Different conditions of heating rate at carbonization were selected. The cRDF was also treated by nitric acid (HNO3) or hydrogen chloride (HCl) prior to the steam activation. Porous properties of the carbons prepared were determined by the nitrogen adsorption method, and the effects of the carbonizing condition and the acid treatment on the properties were elucidated. The hydrophobic surface of the carbons prepared was also confirmed by water vapor adsorption. It was found that the carbons prepared from the RDF were effective for a practical use.