Organic−inorganic hybrids containing methacrylic acid (McOH, CH2═C(CH3)COOH)) modified zirconium tetrapropoxide, Zr(OPrn)4, classed as di-ureasil−zirconium oxo-cluster hybrids, have been prepared and structurally characterized by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies, 29Si and 13C nuclear magnetic resonance (NMR), and atomic force microscopy (AFM). XRD and SAXS results have pointed out the presence of Si- and Zr-based nanobuilding blocks (NBBs) dispersed into the organic phase. Inter-NBBs correlation distances have been estimated for the pure di-ureasil and a model compound obtained by hydrolysis/condensation of Zr(OPrn)4:McOH (molar ratio 1:1): dSi ≈ 26 ± 1 A and dZr ≈ 16 ± 1 A, respectively. In the case of the di-ureasil−zirconium oxo-cluster hybrids, these distances depend on the Zr relative molar percentage (rel. mol. Zr %) (dSi ranges from 18 to 25 A and dZr from 14 to 23 A, as the rel. mol. Zr % increases ...