This study proposes a system to recycle sludge into active cokes and to apply them to removal of contaminants contained in combustion gas or fuel gas produced by gasification of wastes. Fundamental examinations for production of active cokes from sludge and evaluation were conducted. Dry pellets of sludge were heated up in a quartz tube reactor under several atmospheres. The pore structure and the adsorption performance of the produced cokes are examined. The pore structure was found to be influenced by the temperature, the type of flow gas (N-2, CO2 or steam) and heat treatment time, and the active cokes produced by treatment of temperature 823 K for 60 minutes in a steam atmosphere had a largest specific surface area, with a pore diameter of less than 5 nm. The amount of benzene used as an alternative substance of dioxin into the active cokes had a similar quality to a commercial active char produced from coal in terms of adsorption per unit specific surface area.