Background. The Pacific red snapper, Lutjanus peru (Nichols et Murphy, 1922), is one of the most exploited species by artisanal fisheries in Mexico, where it is valued due to its high catch rates and economic value. This study investigated the feeding habits of L. peru in two ecosystems of the southern Gulf of California with contrasting physical and oceanographic conditions. Feeding habits were compared by sex (male or female), size (juvenile or adult), and season (cold or warm), in order to determine whether this species plays the same trophic role in the two ecosystems. Materials and methods. Samples were obtained from the northern Sinaloa coast (SIN region) and south-eastern Baja California Sur coast (BCS region). Percentages by number, weight, and frequency of each food category were determined, and the index of relative importance (%IRI) was calculated to define the main food categories. Diet breadth and diet similarity between sexes, sizes and among seasons were also calculated. Results. A total of 182 stomachs from the SIN region were analysed and 32 prey items from 15 families, 18 genera, and 25 species were identified. According to the index of relative importance (IRI), the most important prey items were the shrimp, Penaeus californiensis (73%); the ostracods, Myodocopida gen spp. (10%); and the squid, Loligo spp. (5%). A total of 233 stomachs from BCS were analysed and 31 prey items from 17 families, 19 genera, and 26 species were identified. The most important prey items according to the IRI were the red pelagic crab, Pleuroncodes planipes (42%); the ostracods, Myodocopida gen spp. (28%); and the shrimp, Penaeus californiensis (20%). Significant differences were identified in the trophic spectra by region, size and season. There were no significant differences by sex. Conclusion. Lutjanus peru displayed a specialist trophic behaviour, with differential utilization of the trophic niche and adequate food resource distribution.