A novel approach based on a molten multicomponent precursor source has been applied for the MOCVD fabrication of high-quality CaCu3Ti4O12 (CCTO) thin films on various substrates. The adopted in situ strategy involves a molten mixture consisting of Ca(hfa)(2)center dot tetraglyme, Ti(tmhd)(2)(O-iPr)(2), and Cu(tmhd)(2)[Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme) 2,5,8,11,14-pentaoxapentadecane; Htmhd = 2,2,6,6-tetramethyl-3,5-heptandione; O-iPr) isopropoxide] precursors. Film structural and morphological characterizations have been carried out by several techniques [X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM)], and in particular the energy filtered TEM mapping and X-ray energy dispersive (EDX) analysis in TEM mode provided a suitable correlation between nanostructural properties of CCTO films and deposition conditions and/or the substrate nature. Correlation between the nanostructure and optical/dielectric properties has been investigated exploiting spectroscopic ellipsometry.