Yttrium oxide thin film deposition by atomic layer epitaxy (ALE) was studied at 200–425 °C using Y(thd)3, Y(thd)3(bipyridyl), or Y(thd)3(1,10-phenanthroline) (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) as an yttrium precursor, and ozone as an oxygen source. All yttrium precursors were analyzed by thermogravimetry/differential thermal analysis (TG-DTA) and mass spectrometry (MS). Soda lime glass and Si(100) were used as substrates. With all precursors, a constant deposition rate of 0.22–0.23 Å (cycle)–1 was observed at 250–350 °C on both substrates, indicating a surface-controlled growth and similar surface species at the deposition temperatures used. The effect of growth parameters, such as reactant pulsing times, was investigated in detail at 350 °C using Y(thd)3. Deposited films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to determine crystallinity and surface morphology, while ion-beam analysis and X-ray photoelectron spectroscopy (XPS) were used to analyze stoichiometry and impurity levels. Infrared (IR) measurements were performed to determine the type of carbon impurity. Crystalline films with a (400) dominant orientation were obtained when depositions were carried out within the ALE window (temperature range of 250–375 °C), but films deposited below 250 °C were nearly amorphous. Preferential orientation changed from (400) to (222) when deposition temperatures were raised slightly above the ALE window to 375 °C, where a partial decomposition of Y(thd)3 probably takes place. Judging from the impurity levels of the films and growth rates, the adducting of Y(thd)3 does not bring about any advantages in the ALE growth of Y2O3.