A wide variety of structurally related Schiff base and acid amide compounds and low-molecular-weight polymers were synthesized. The comparative thermal stabilities of the products in air were investigated by thermogravimetric analysis. Several of the Schiff bases prepared from aromatic diamine compounds and terephthalaldehyde exhibit unusually good resistance to decomposition by heat. The influence of chemical structure on thermal stability is shown, and the important factors that may serve as a guide for the tailor-making of high-molecular-weight polymers with superior heat resistance are discussed.