Disclosed is a process for producing a polyamic acid solution by reacting a diamine component consisting essentially of 20 mol % to 80 mol % of p-phenylenediamine and 80 mol % to 20 mol % of diaminodiphenyl ether with a tetracarboxylic acid component consisting essentially of 10 mol % to 60 mol % of 2,3,3′,4′-biphenyltetracarboxylic dianhydride and 90 mol % to 40 mol % of 3,3′,4,4′-biphenyltetracarboxylic dianhydride in a solvent, comprising: a first step in which a diamine component is reacted with a molar excess of a tetracarboxylic acid component in a solvent containing more than ⅓ mole of water per mole of the tetracarboxylic acid component, whereby preparing a polyamic acid solution; and a second step in which a diamine component, or a diamine component and a tetracarboxylic acid component are added to the polyamic acid solution obtained in the first step so that the molar amount of the diamine component is substantially equal to the molar amount of the tetracarboxylic acid component, and then the diamine component and the tetracarboxylic acid component are reacted.