Most atomic layer deposition (ALD) processes for metal oxides involve the use of a metal precursor and an oxygen source, such as H2O, O3, or an O2 plasma. These ALD processes lead to the formation of an undesirable interfacial oxide during deposition on semiconductor surfaces. As an alternative, some metal oxides other than TiO2 have been deposited using metal alkoxides as the oxygen source. In this article, we report on the ALD of TiO2 using TiCl4 and titanium tetraisopropoxide (TTIP) as precursors. Our surface infrared spectroscopy data shows that over the temperature range of 150–250 °C and the duration of a typical ALD cycle (∼1–10 s), in both half-reaction cycles, the surface reaction mechanism is dominated by alkyl-transfer from the TTIP ligands to Ti-Cl species. At 250 °C, which is the onset for TTIP thermal decomposition, the contribution of the direct decomposition reaction to film growth is negligible. The growth per cycle, ∼0.7 Å at 200 °C, is higher than H2O-based ALD of TiO2 from either TiCl4 or TTIP, but similar to O2-plasma-based processes. X-ray photoelectron spectroscopy data show TiO2 films with only the +4 oxidation state of Ti, and the Cl content is estimated to be 2.5–3.5%. UV–Vis spectroscopy shows a band gap of ∼3.0 eV, which is comparable to the values reported in the literature for amorphous TiO2 thin films.