The diamagnetic response of tetracene is exploited to increase the in-plane orientation of thin films grown by organic molecular beam deposition, while applying a magnetic field of 0.2 T parallel to the surface of the silica and potassium hydrogen phthalate substrates. The combined spectroscopic analysis of the films in the UV/visible region and morphological investigation of their surface performed by atomic force microscopy demonstrate a substantial increment of the film order when the magnetic field is applied along the c axis of potassium hydrogen phthalate, in agreement with the anisotropic magnetic susceptibility of tetracene.