We investigated surface stabilities and stresses of beta-Sn and their consequences to the nanowire structure through density-functional theory calculations. beta-Sn nanowires are well known to grow along the [1 0 0] direction. Even though the (1 0 0) and (0 1 0) planes are equivalent in bulk, the surface stresses are found to induce the anisotropic deformation. Along the surface zigzag bond chain direction, large negative surface tensions are found, combined with a linearization tendency of the zigzag bond chains. The negative surface tensions are not typical on metal surfaces and results in the elongation of the beta-Sn metal nanowires. (C) 2009 Elsevier B. V. All rights reserved.