TiO2 is one of the wonder materials that possess extraordinary engineering versatility in terms of nanostructures, shapes and morphology. TiO2 nanomaterials have shown superior antibacterial capability, it is however still unclear about the intrinsic dimensional effects on antibacterial mechanisms. This study reported a fundamental antibacterial mechanism about the intrinsic antibacterial capabilities of the engineered nanostructured TiO2 materials (ENMs) - from three aspects 1) the structures of such nanoparticles, rods, tubes, fibres and spheres; 2) sizes/diameters/length of the ENMs; 3) combined effect due to dimensions and structures. Experimental results revealed that, the 1 D nanotubular TiO2, being the smallest individual ENMs possessed the highest toxicity towards E. coli; further studies showed that 3 D dendritic nanostructure incorporated with 1 D ultrathin TiO2 nanorods had the highest antibacterial efficiency. Comparative studies have suggested that, the well-engineered 3 D TiO2 nanomaterials (microspheres) with enhanced surface properties such as evenly grown 1 D sub-structures were more aggressive than the cluster aggregated 1D nanomaterials. In-depth research concluded that with well-controlled nanorods density and length, the integrated 3 D ENMs exhibited most efficient antibacterial activities. Such results could benefit the future antibacterial applications and the agent fabrications.