A series of new strictly alternating aromatic poly(ester-imide)s having inherent viscosities of 0.20-0.98 dL/g was synthesized by the diphenylchlorophosphate (DPCP) activated direct polycondensation of the preformed imide ring-containing diacid, 3,3 -bis [4-(trimellitimidophenoxy)phenyl] phthalide (I), with various bisphenols in a medium consisting of pyridine and lithium chloride. The diimide-diacid I was prepared from the condensation of 3,3-bis [4-(4-aminophenoxy)phenyl] phthalide and trimellitic anhydride, Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc), Transparent and flexible films of these polymers could be cast from their DMAc solutions. The cast films had tensile strengths ranging 66-105 MPa, elongations at break from 7-10%, and initial moduli from 1.9-2.4 GPa. The glass-transition temperatures of these polymers were recorded between 208-275 degrees C, All polymers showed no significant weight loss below 400 degrees C in the air or in nitrogen, and the decomposition temperatures at 10% weight loss all occurred above 460 degrees C.