Alternative novel precursor chemistries for the vapor phase deposition of rare-earth (RE) oxide thin films were developed by synthesising the homoleptic guanidinate compounds tris(N,N′-diisopropyl-2-dimethylamidoguanidinato)-scandium(III) [Sc(DPDMG)₃] (1), tris(N,N′-diisopropyl-2-dimethylamidoguanidinato)-erbium(III), [Er(DPDMG)₃] (2) and tris(N,N′-diisopropyl-2-dimethylamidoguanidinato)-yttrium(III), [Y(DPDMG)₃] (3). All three compounds are monomeric as revealed by single crystal X-ray diffraction (XRD) analysis, nuclear magnetic resonance (NMR) and electron impact mass spectrometry (EI-MS). The thermal analysis revealed that the compounds are volatile and very stable under evaporation conditions. Therefore the complexes were evaluated as precursors for the growth of Sc₂O₃, Er₂O₃ and Y₂O₃ thin films, respectively, by metal–organic chemical vapor deposition (MOCVD). Uniform Sc₂O₃, Er₂O₃ and Y₂O₃ films on Si(100) substrates with reproducible quality were grown by MOCVD by the combination of the respective guanidinate precursors and oxygen in the temperature range 350–700 °C. The structural, morphological, compositional and electrical properties of the films were investigated in detail. The most relevant film properties are highlighted in relation to the distinct advantages of the novel precursor chemistries in comparison to the commonly used literature known RE precursors. This study shows that compounds 1–3 are very good precursors for MOCVD yielding Sc₂O₃, Er₂O₃ and Y₂O₃ thin films which are stoichiometric and display suitable electrical properties for their potential use as high dielectric constant (high-k) materials.