The favourite adsorption site of ethylene on the Ni (110) surface at high and low coverages was investigated by theoretical calculation. In the cluster calculations a partial optimization of adsorbate geometry has been carried out. At low coverage the ethylene molecule occupies approximately the midway between the short-bridge and atop sites. The C—C axes of molecules are almost parallel to the ridges and are offset in the direction, the angle of C—C axis with respect to the Ni surface plane is about 10°. The C—C bond length is 0151 nm. At a high coverage (05ML), ethylenes form a c (2×4) phase. The local adsorption sites of two ethylene molecules in a surface unit mesh are found to be quite similar to that at low coverage, but the C—C bond lengths are 0142 nm and 0142 nm, respectively.