A new-type tetraimide-dicarboxylic acid (I) was synthesized starting from the ring-opening addition of p-aminobenzoic acid (p-ABA), 4,4'-oxydiphthalic anhydride (ODPA), and 4,4'-methylenedianiline (MDA) at a 2:2:1 molar ratio in N-methyl-2-pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of poly(amide-imide-imide)s (IIIa-i) with inherent viscosities of 0.78-1.45 dL/g was prepared by triphenyl phosphite-activated polycondensation from the tetraimide-diacid I with various aromatic diamines (IIa-i) in a medium consisting of NMP, pyridine, and calcium chloride. Most of the polymers were readily soluble in a variety of organic solvents such as NMP, N,N-dimethyl acetamide, dimethyl sulfoxide, and even in less polar m-cresol. Compared with those of the corresponding poly(amide-imide)s IVa-i, the solubilities of poly(amide-imide-imide)s IIIa-i were greatly improved. Polymers IIIa-h afforded tough, transparent, and flexible films, which had tensile strengths ranging from 87 to 107 MPa, elongations at break from 9% to 14%. and initial moduli from 2.0 to 2.4 GPa. The glass transition temperatures of polymers were recorded at 270degreesC-309degreesC. They had 10% weight loss at temperatures in the range of 540degreesC-570degreesC and left more than 52% residue even at 800degreesC in nitrogen.