Electrospun TiO2 nanofibers, consisting of anatase phase TiO2 single-crystalline crystallites with sizes of similar to 10 nm, were impregnated into an Al 1100 alloy by the technique of friction stir processing (FSP). The studies of the resulting TiO2-Al composite revealed that the electrospun TiO2 nanofibers with diameters of similar to 200 nm were broken into nanoparticles during FSP; the in situ generated pristine surfaces led to the interfacial reaction between TiO2 and Al and resulted in the formation of strong interfaces between the electrospun TiO2 nanoparticles and the Al 1100 matrix. This was evidenced by the Fact that the filler-matrix fracture always occurred on the Al matrix side in the interfacial region. Consequently, the TiO2-Al composite made from the electrospun TiO2 nanofibers possessed a significantly higher Vickers hardness than that made from a commercially available anatase phase TiO2 nanopowder, of which the organic and/or carbonaceous contaminants on the surface impeded the interfacial reaction between TiO2 and Al during FSP.