We present a first-principle study on the atomic and electronic structure of II–VI wurtzite ZnO unsaturated nanowire and examine the dependence of surface stress on nanowire lateral size and shapes (hexagonal, triangular and tube-like) with diameter up to 31 Å. We investigate the unsaturated dangling bond state in the region of bandgap with varying the wire’s diameter. We also calculated the surface formation energy and find that it decrease with increasing the wire diameter and a greater stability (lower surface formation energy) comes with hexagonal wires. Young’s modulus calculation and various tensile tests have been applied to show the mechanical properties. The electronics properties of these wires (e.g. band structure, Density of State, charge transfer via Mulliken population analysis) also exhibit wire’s diameter dependence behaviors.