A process for producing a bistrimellitic imide of the formula (2) ##STR1## wherein X is an aliphatic group having at least 2 carbon atoms, an alicyclic group or an aromatic group,which comprises reacting a trimellitic anhydride with a diamine of the formula (1)H.sub.2 N--X--NH.sub.2 (1)wherein X is as defined above, in the presence of a solvent mixture containing an aprotic polar solvent and an aromatic hydrocarbon solvent which can be distilled azeotropically with water, the amount of the aromatic hydrocarbon solvent being 10 to 90% by weight based on the total weight of these two solvents.