Abstract: A base film for a photographic film, wherein (a) the refractive index (nz) in the thickness direction is at least 1.498, (b) the haze value is 2.0% or less, (c) the base film has one direction in which the tan.delta. value, at 80.degree. C. by tensile viscoelasticity at 0.05 Hz, is 0.09 or less, (d) the anti-curling ratio at 70.degree. C. is at least 45%, (e) the thickness is in the range of from 40 to 120 .mu.m, and (f) the base film is formed from polyethylene-2,6-naphthalendedicarboxylate as a substantial raw material. This base film has various performances such as anti-curling properties, transparency and lubricity, suitable for use in a photographic film.