Poly(amide-imide) (PAI) could be synthesized in regular segment order from trimellitic anhydride (TMA) and various aromatic diamines. By different processes, PAI(h-h-t-t) containing alternating (amide-amide)-(imide-imide) sequences and PAI(h-t) containing amide-imide sequences could be obtained through direct polycondensation. Comparison of PAI(h-h-t-t) and PAI(h-t), which had different sequence orders and were prepared from TMA and 12 diamines, showed that the latter had better solubility and needed less quantity of solvent and salt (CaCl2) during polymerization, but both two series PAI using p-substituted diamines (e.g., p-phenylenediamine) showed poor solubility. Series PAI(h-h-t-t) possessed larger initial modulus but smaller elongation at break than series PAIh-t. For the thermal properties, most of series PAIh-t had glass transition temperatures higher than corresponding series PAI(h-h-t-t), but these two series were similar in the 10% weight loss temperatures and the char yields at 800 degreesC in nitrogen.