Thermostable polyamideimides with inherent viscosity of 1.02-1.50 dL/g were synthesized from reacting of diamine-terminated aromatic amide prepolymer with various diisocyanate terminated imide prepolymers. The imide prepolymer was prepared by using 4,4’-diphenylmethane diisocyanate to react with 3,3’,4,4’ benzophenonetetracarboxylic dianhydride, 3,3’,4,4’-sulfonyl diphthalic anhydride, or 4,4’-oxydiphthalic anhydride using the direct one-pot method to improve their solubility. Almost all of the polyamideimides were generally soluble in a wide range of organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and pyridine at room temperature. Polymers with high imide content required high temperatures to dissolve. All polyamideimides had a glass transition temperature of 223-352 degrees C and showed a 10% weight loss temperature of 415-575 degrees C in air and 424-583 degrees C in nitrogen atmosphere. The tensile strength, elongation at break, and initial modulus of polymer films ranged from 61 to 108 MPa, 5 to 10%, and 1.54 to 2.50 GPa, respectively. These copolymers were partly crystalline in structure as shown by X-ray patterns.