PURPOSE: To prepare solid fuel without the need of any binder and without generation of harmful gas, by granulating dehydrated organic sludge, molding the dried granules by extrusion molding at a temperature and under a pressure which cause plasticization and then drying cut pieces by forced draft.

CONSTITUTION: Organic sludge (e.g. those produced in pulp and fermentation industries) is dehydrated and crushed into small granules. The granules are dried to a water content of 5W25wt%. The dried granules are molded by extrusion molding. The formed product is cut and the cut pieces are cooled by forced draft into pellets of solid fuel. It has been a general practice to mix dehydrated and dried organic sludge with a binder (e.g. coal, tar, pitch or waste oil) for molding, but the method has a demerit in that it requires a large amount of binder which generates harmful gas in combustion. This invention eliminates such disadvantages.