The adsorption of C2H4 on the FeNi(1 1 1) alloy surface has been studied by ASED-MO tight binding calculations. The C2H4 molecule presents its most stable geometry with the C=C bond axis parallel to the surface along the [1, -1, 0] direction, bonded on top Fe atom and bonded along a Fe-Fe bridge site. As a consequence, the strength of the local Fe-Fe bond decreases between 37 and 62% of its original bulk value. This bond weakening is mainly due to the new C-Fe interactions however no Fe3C carbide formation is evidenced on surface. The Fe-Ni and Ni-Ni superficial bonds are only slightly modified. (C) 2010 Elsevier B.V. All rights reserved.