We report a study of the effect of nitrogen ion bombardment on the optical properties of anatase TiO2ultrathinfilms, particularly the band gap energy. The TiO2films were prepared by a sol-gel method and dip-coatingprocess. The as-prepared TiO2films were then exposed to a+N2low-energy ion beam from a microwave electroncyclotron resonance (ESR) ion source. Raman and spectroscopic ellipsometry (SE) analysis were performed onTiO2films prepared at different+N2exposure times. The Raman measurements reveal the conservation of theanatase TiO2crystalline structure after the ion beam exposure. From a detailed ellipsometric study, the thicknessof layers, the dielectric function, the band gap and the Urbach energies were determined. The obtained resultsshow an increase of the TiO2band gap with the decrease of thickness offilms during+N2exposure time. The bandgap energy was blue shifted from 20 meV to 140 meV as the exposure time was increased from 5 min to 20 minwhen the thickness was decreased from 30 nm to 21 nm. This increasing of band gap energy could be explainedby the thickness effect. From the band tail, the Urbach energy was also affected by+N2ion beam. These results arein good agreement with the observed broadending of the Raman band the OeTieO bending vibration mode, asthe exposure time increases.