A method for producing a carbonaceous material-polymer composite material in which a polymer can be easily grafted to a carbonaceous material and a carbonaceous material-polymer composite includes the steps of: preparing a mixture containing a carbonaceous material and at least one polymer A of a polymer obtained by polymerizing a cyclic disulfide compound and a polymer obtained by polymerizing a cyclic disulfide compound and a radical polymerizable functional group-containing monomer; and heating the mixture at a temperature range of (D-75)° C. or higher and a decomposition termination temperature or lower when a decomposition start temperature of the polymer A is defined as D° C., and a carbonaceous material-polymer composite material obtained by the production method wherein a monomer and/or a polymer derived from the polymer A is grafted to a carbonaceous material.