PURPOSE: To obtain a polyimide of a low coefficient of thermal expansion, by imidating a specified polyamic acid in the presence of a carboxylic acid monoanhydride and an aromatic nitrogen-containing compound under specified conditions.

CONSTITUTION: A polyamic acid obtained by reacting 3,3',4,4'-biphe nyltetracarboxylic dianhydride with an aromatic diamine comprising p- phenylenediamine and 4,4'-diaminodiphenyl ether in an organic polar solvent is reacted in the presence of a carboxylic acid monoanhydride and an aromatic nitrogen-containing compound under the following conditions. Namely, the polyamic acid is imidated at a temperature in the range of 80W250°C in the presence of 0.2W5mol of the carboxylic acid monoanhydride and 0.005W5mol of the aromatic nitrogen-containing compound per mol of the amide bond of the polyamic acid. In this way, it is possible to produce a polyimide having excellent mechanical properties (tensile strength ≥ 20kg/mm2) and a coefficient of thermal expansion as low as 3×10-5/°C or below.