TiO 2 (30–80 wt.%) and ZrO 2 (48–75 wt.%) were inserted inside the pores of SBA-15 mesostructured silica host by chemical solution decomposition (CSD) or internal hydrolysis (IH) of the corresponding alkoxides. Both methods yielded composites with 85–94% TiO 2 crystallinity (anatase). In case of ZrO 2, CSD yielded >95% crystallinity (tetragonal phase), while IH gave an amorphous ZrO x -phase that does not crystallize up to 1073 K. The guest Ti(Zr)-oxide phases did not block the SBA-15 pores, and their surface was fully accessible for nitrogen adsorption. Calcination in air of TiO 2/SBA-15 and ZrO 2/SBA-15 (CSD) composites up to 1073 K did not change the nanocrystals structure and slightly increased the domain size derived from XRD data from 5.0–8.5 to 6–10 nm for TiO 2 (IH and CSD) and from 4.5 to 6.5 nm for ZrO 2 (CSD). After the same treatment the crystals domain size of bulk reference TiO 2 increased to >100 nm with full conversion to rutile polymorph and of reference bulk ZrO 2––to 20–25 nm with partial conversion to monoclinic modification. Thorough characterization of the texture, structure, location and dispersion by HRTEM, SAXS, EDS, SEM, XRD, N 2-adsorption methods allowed evaluation of the assembling mode of TiO 2 and ZrO 2 inside SBA-15 nanotubes: amorphous layer, ensemble of small 4–5 nm crystals (TiO 2-IH and ZrO 2-CSD) or single large 8.5 nm crystals (TiO 2-CSD).