A series of novel thermally stable poly(amide-imide)s (PAIs) based on non-coplaner diimide-diacid (DIDA) monomer is synthesized. These polymers are characterized by elemental analysis, FT-IR, H-1-NMR, C-13-NMR and P-31-NMR spectroscopic techniques and their physical and thermal properties are also studied. Four different dianhydrides pyromellitic anhydride (PMDA)/3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA)/1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA)/4,4'-oxydiphthalic anhydride (ODPA) and amino acid l-tryptophan are used to synthesize DIDA. The polymerization of DIDA with phosphorus containing triamines having phenyl moieties gives poly(amide-imide)s. The synthesized polymers are obtained in high yield and possessed inherent viscosity in the range 0.66-0.98 dL/g. These polymers display higher solubility in polar aprotic solvents, such as DMSO, NMP and DMF. In addition, the absorption edge values (lambda (o)) obtained from their UV curves are determined, and all the resulting poly(amide-imide)s films exhibited high optical transparency. The glass transition temperature (T (g)) of these polymers is recorded in the range 211-265 A degrees C, initial decomposition temperature in excess of 435 A degrees C and char yield at 800 A degrees C in nitrogen ranged from 52 to 70 %. Wide angle X-ray diffraction showed that all the polymers are almost amorphous.