The one-pot method polymerization of polyimide was carried out from 3,3’,4,4’-biphenyl tetracarboxylic dianhydride (BPDA) and 4,4’-oxydianiline (ODA) by the use of p-chlorophenol as the solvent. The behavior of the polymerization was compared with that of the two-step method. The imidization reaction in the one-pot method proceeds completely in this system at even a low temperature such as 100 degrees C. In the course of the film preparation from the solution, the embrittlement occurs when the film is prepared from polyamic acid solution, while it does not occur in the case of that from the solution of the one-pot method. A molecular weight of polyimide film is almost the same as that of precursor polyimide in the solution. In the same way, that of polyimide film is almost the same as that of precursor polyamic acid. The mechanical properties of the polyimide film prepared by the one-pot method are similar to those by the two-step method.