PURPOSE: To prepare industrially in a good yield the title copolymer by copolymerizing indene with maleic anhydride by using a specified reaction solvent by the radical polymn. process.

CONSTITUTION: In the preparation of a copolymer consisting of indene and maleic anhydride by the radical polymn. process in a solvent, it is pref. to use a solvent dissolving the formed indene-maleic anhydride copolymer and being inert to the reaction for the purpose of preventing the tendency that stirring becomes difficult in a polymn. vessel and it is practically ketone solvent (e.g., acetone or methyl ethyl ketone). Copolymn. is performed by heating under reflux while stirring and the temp. is returned to room temp. The title copolymer is recovered by pouring the reaction mixture in a poor solvent consisting of an aliph. hydrocarbon and/or a naphthene hydrocarbon. The title copolymer can be industrially prepd. in a high yield.