Two series of phosphorus-containing aromatic poly(ester amide)s with inherent viscosities of 0.46-3.20 dL/g were prepared by low-temperature solution polycondensation from 1,4-bis(3-aminobenzoyloxy)-2-(6-oxido-6H-dibenz(c,e)(1,2)-oxaphosphorin-6-yl)naphthalene and 1,4-bis(4-aminobenzoyloxy)-2-(6-oxido-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)naphthalene with various aromatic diacid chlorides. All the poly(ester amide)s were amorphous and readily soluble in many organic solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP). Transparent, tough, and flexible films of these polymers were cast from DMAc and NMP solutions. Their casting films had tensile strengths of 71-214 MPa, elongations to break of 5-10%, and initial moduli of 2.3-6.0 GPa. These poly(ester amide)s had glass-transition temperatures of 209-239 degreesC (m-series) and 222-267 degreesC (p-series). The degradation temperatures at 10% weight loss in nitrogen for these polymers ranged from 462 to 489 degreesC, and the char yields at 800 degreesC were 55-63%. Most of the poly(ester amide)s also showed a high char yield of 35-45%, even at 800 degreesC under a flow of air. The limited oxygen indices of these poly(ester amide)s were 35-46.