This invention relates to a process for preparing polyimide having good heat-stability and excellent flowability in a molten state. The polyimide is prepared by reacting 3,3′-diaminobenzophnone or bis(3-aminophenyl)sulfone, tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and bis(3,4-dicarboxyphenyl) ether dianhydride; and dicarboxylic anhydrides such as glutaric anhydride, 1,2-hexanedicarboxylic anhydride, phthalic anhydride and 3,4-benzophenonedicarboxylic anhydride. The molar ratio of aromatic diamine : tetracarboxylic dianhydride : dicarboxylic anhydride is 1 :(0.9 to 1.0) : (0.001 to 1.0).