A series of new polyamides were synthesized by direct polycondensation of the 4,9-diamantane dicarboxylic acid (I) with various aromatic diamines in N-methyl-2-pyrrolidone (NMP) containing lithium chloride. The polyamides had inherent viscosities of 0.56-1.85 dL/g. Dynamic mechanical analysis revealed the polymers IIIa-IIId to have main melting transitions at 403, 431, 423, and 452 degrees C, respectively. Moreover, these polymers were quite stable at high temperatures and maintained good mechanical properties (G’ = ca. 10(8) Pa) up to temperatures close to the main transition well above 400 degrees C. Although the polyamides contained rigid 4,9-diamantyl moieties in the main chain, the tensile properties of the polyamides showed toughness. Elongations of polyamides IIIa and IIIb reached 38.3 and 31.7%, respectively, before breaking. A glass transition was not observed. However, polyamide IIIc shows a melting transition with a sharp endothermic peak at 423 degrees C by DSC measurement. Additionally, the introduction of 4,9-diamantyl units into the polyamide backbone resulted in polyamides with high thermal stability and good mechanical properties.