Using resistive heated method, Ti films of different thickness ranging from 10 to 200 nm were deposited and post-annealed at a temperature of 473K with a flow of oxygen. The optical properties were measured by transmission spectroscopy in spectral range of 200-2500 nm. The optical functions were obtained from the Kramers-Kronig analysis of the reflectivity curves. The effective medium approximation analysis was employed to establish the relationship between the nano-structure and Effective-Media Approximation (EMA) predictions.It was found the temperature of deposition and thefilm thickness play important roles in the nano-structure of the film and cause significant variations in the optical behaviour of thin Titanium oxide films.