Abstract: A method for treating a waste high-polymer mixture by fractionating the mixture consisting essentially of five groups of high polymers, i.e., polyolefinic, polystyrenic, polyvinyl-chloride, thermosetting, and natural high polymers, taking advantage of their dissimilar solubilities in different organic solvents, characterized in that the mixture is brought into contact with o-xylene, p-xylene, or m-xylene, the solvents being used either singly or in a combination of two or more, at temperatures within a certain range or ranges to dissolve and fractionate the polystyrenic and polyolefinic high polymers, and the polyvinyl chlorides in the remainder are dissolved and fractionated by using at least one solvent selected from the group consisting of tetrahydrofuran, cyclohexanone, dioxane, and methylethylketone and at a temperature within a certain range, whereby the waste mixture is fractionated into the groups of polyolefinic, polystyrenic, polyvinyl-chloride, thermosetting, and natural high polymers.