To provide a method for producing an imide polymer having high compatibility with other thermoplastic polymers in blending without converting an acid group and an acid anhydride group to a non-acid group and a non-acid anhydride group with an alkylation agent and an esterification agent by decreasing the amount of the acid group and the acid anhydride group in the imide polymer produced by reacting an acrylic acid polymer with an imidizing agent in an extruder.

The acid value of an imide polymer can be decreased to ≤0.4 while improving the imidization ratio to ≥30% by carrying out the imidization reaction for a long period by setting the reaction time in the reaction zone of an extruder to be longer than 1,000 sec.