The mechanisms governing the tensile behavior of TiO(2) nanowires were studied by molecular dynamics simulations. Nanowires below a threshold diameter of about 10 A transformed into a completely disordered structure after thermodynamic equilibration, whereas thicker nanowires retained their crystalline core. Initial elastic tensile deformation was effected by the reconfiguration of surface atoms while larger elongations resulted in continuous cycles of Ti-O bond straightening, bond breakage, inner atomic distortion, and necking until rupture. Nanowires have much better mechanical properties than bulk TiO(2). Nanowires below the threshold diameter exhibit extraordinarily high stiffness and toughness and are more sensitive to strain rate.