The phases present and their crystal structure and microstructure in the nanocrystalline SnO2-TiO2 system were studied in the compositional range Sn1-xTixO2 (0.0x0.9). There is an apparent increase in the solubility limits in the solid solution compared to bulk crystalline SnO2-TiO2. No two phase region was observed with increasing TiO2 content. Electron energy loss spectroscopy, infrared spectroscopy (FTIR), and X-ray diffraction (XRD) of the nanopowders showed that the apparent increase in solubility is related to the systematic Ti4+ segregation on the particle surface (surface excess) at the SnO2-rich side, avoiding the nucleation of a second phase even at high Ti4+ contents. Is this finding in accord with Raman spectra, which suggest localized Ti-rich sites in the absence of a second crystalline phase. Ti4+ surface excess is also lead to a modification of the surface hydroxyls and a decrease in the crystallite size of the nanoparticles (with a concomitant increase in surface area), with expected implications to catalytic and sensorial properties of these nanoparticles.