When preparing carbon artefacts from heavy oils of petroleum or coal origin, removal of undesirable components or recovery of desirable components from raw materials or intermediates is usually required so as to improve the quality of the final products. Such removal or recovery operation is conventionally done by filtration. In the past, regeneration of filters clogged with solid carbonaceous materials inevitably formed by the filtration operations is difficult and troublesome procedures. Herein disclosed is a simple and effective process for regenerating filters clogged with solid carboneceous materials, characterized by treating the filter medium in an aqueous solution of hydrogen peroxide with heating and then optionally conducting ultrasonic washing in water or a solvent. By this simple process, clogged filters can be regenerated completely to show the same filtration performance as new filters.