This paper reports on the effect of low energy He+ion‐beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Films are prepared by vacuum evaporation during ion bombardment at room temperature. The structure of the film is controlled by the kinetic energy and current density of the ions. The colorless and transparent crystalline films preferentially oriented with their {001} plane parallel to the substrates are obtained by bombardment of 350 to 500 eV, 60 nA/cm2He+ions. Ion‐beam irradiation of the higher ion current density enhances intermolecular chemical reactions and, as a result, a crystalline polymer with its {001} plane parallel to the substrate is produced.