Provided is a biaxially oriented, unidirectionally long polyethylene-2,6-naphthalenedicarboxylate film having the following characteristic properties;(A) both the Young's modulus in the longitudinal direction and the Young's modulus in the transverse direction are at least 600 kg/mm.sup.2, and the Young's modulus in the longitudinal direction is greater than the Young's modulus in the transverse direction,(B) the heat shrinkage factor in the transverse direction when the film has been treated under no load at 105.degree. C. for 30 minutes is at least 1%, and(C) the surface roughness Ra of one surface of the film is up to 5 nm, anda magnetic recording tape obtained by forming a thin magnetic metal film on the above film undergoes no curling, has high coercive force, has excellent electromagnetic conversion characteristic and permits high-density recording for a long period of time.