Abstract: The improved method of converting organic wastes to valuable resources comprises a methane fermentation step (4) in which a slurry of organic waste is retained for fermentation in an anaerobic digester to thereby generate a methane-containing gas and a fermentation slurry, a hydrothermal treatment step (11) in which the fermentation slurry is subjected to a hydrothermal reaction to thereby generate a carbon slurry, and a concentrating step (14) in which an aqueous phase is separated from the carbon slurry to thereby yield a concentrated carbon slurry having a high heating value. The method is capable of performing an effective hydrothermal treatment on a slurry of low water content, prevents the slurry from putrefaction during retention in the process and it yet is capable of effective treatment of the aqueous phase of the slurry after the hydrothermal treatment.