Ultrathin (<100 Angstrom) titanium oxide films have been synthesized on the Mo(100) surface and characterized using various surface science techniques. Epitaxial TiO2 films of varying film thickness were prepared by evaporating titanium in an oxygen background (5X10(-7) Torr) between 500 and 700 K, followed by annealing to 900-1200 K. The growth, composition, and structure of the TiO2 films have been investigated using ion scattering spectroscopy (ISS), x-ray photon spectroscopy (XPS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunnel microscopy (STM). A (2 root 2X root 2)R45 degrees LEED pattern was observed after annealing 4.7, 15, and 90 Angstrom film thicknesses to 900-1200 K in vacuum. LEED and STM results show that the TiO2 films order along the [010] and [001] directions of the Mo(100) substrate. XPS data show that unannealed titanium oxide films exhibit only the Ti4+ valence state, whereas annealed titanium oxide films are partially reduced and exhibit the Ti3+ and Ti2+ states, as well. SS measurements of unannealed titanium oxide films show that TiO2 films wet the Mo(100) surface well.