ABSTRACT. – The stomach contents of fifty swordfish, Xiphias gladius, caught in the western Mediterranean Sea by commercial semi-pelagic longline were analysed to determine their diet and feeding preferences. Post-hoc multiple comparison tests among prey species indicated that blue whiting, Micromesistius poutassou, was the main prey followed by Notoscopelus elongatus, Myctophum punctatum, and the cephalopods Todarodes sagittatus and Ancistroteuthis lichtensteinii. Thus, mesopelagic prey were the main group making up the diet representing over 94 % in terms of biomass. The diversity of prey species reflects the trophic plasticity of the swordfish, with bathymetry and species distribution key factors in their diet preferences. The trophic interaction with the three most common top predators in the area, Tursiops truncatus, Stenella coeruleoalba and Grampus griseus was very low, and there was no evidence of interaction with fisheries. The present study indicates resource partitioning as a strategy to reduce competition among sympatric top predators.