To provide a method for producing a phase difference film excellent in optical quality and appearance having decreased minute foreign matters present in the film.

In this method, the phase difference film is produced by cast forming a polysulfone resin soln. The content of condensation products of 4,4'- dichlorodiphenyl sulfone and the sodium salt of bisphenol-A shown by the formula present in the polysulfone resin soln. before cast forming is controlled to ≤0.5 wt.% of the polysulfone resin.