The blue shark (Prionace glauca) is the most landed shark species in Peruvian shark fisheries, representing 42% of total landings. Despite its importance for fisheries, the ecological role of the blue shark in Peruvian waters remains poorly understood. Therefore, in this study, we aimed to assess the food habits of blue sharks off northern Peru through stomach content analysis. Between February and December of 2015, 143 stomachs were collected and 28 found to be were empty. Individuals measured from 110.0 to 299.4 cm in total length. The results indicate that blue sharks have epipelagic and mesobathypelagic feeding habits, preying upon a wide number of prey taxa (42 species) but with a diet dominated by cephalopods, especially Argonauta spp. and Ancistrocheirus lesueurii. Diets differed by size class and location, suggesting that longitudinal movements are related to increments in body size. In addition, we propose that blue sharks scavenge for food on the basis of finding the cyprid larval stage and juvenile cosmopolitan duck barnacle (Lepas anatifera) associated with the prey item ‘un-identified cephalopods.’ The present study contributes new information on the diet of blue sharks.