Heat treatment of films obtained by interfacial condensation of 4,4′-methylene dianiline (MDA) or ethylene diamine (EDA) in water and 1,2,4,5-benzenetetra acyl chloride (BTAC) in dichloromethane were studied by Fourier transform infrared spectroscopy (FTIR), 1H-and 13C-nuclear magnetic resonance (NMR), fast atom bombardment mass spectrometry (FABMS), an elemental analyzer, and differential scanning calorimetry (DSC). The reaction scheme for forming the polyimide is presented. Films were synthesized from the aromatic diamine and from the aliphatic diamine system. Both must go through two-stage thermal treatment to form the structure of the imide. The first stage of this reaction is the imidization of the polyamic acid, and the second is the reaction to imidization of the functional amide group linked to the neighboring carbon on the benzene ring. After thermal treatment, the films will maintain good heat resistance. The difference between the mentioned interfacial synthetic polyimide and the conventional synthetic polyimide is that no isoimide and anhydride groups are found in the former. But the thickness of the film is limited by the nature of interfacial polymerization. In our reaction system, the maximum thickness of the film did not exceed 20 μm.