The present invention provides a birefringent film that hardly generates cracks even when the film is exposed under a high-temperature and high-humidity environment for a long period of time. The birefringent film of the present invention is a film containing, as a major component, a lyotropic liquid crystalline polycyclic compound containing an acenaphtho[1,2-b]quinoxaline derivative unit in a molecular structure and having a molecular weight of 500 or higher. The birefringent film of the present invention preferably has a refractive index ellipsoid showing a relationship of nx.gtoreq.nz>ny, and more preferably has an in-plane birefringence of 0.01 or higher at the wavelength of 590 nm.