ABSTRACT: Prey energy density values are crucial inputs to bioenergetic consumption models. Vertebrate predators in the northwest Atlantic consume a variety of prey species, but the proximate composition (PC; proportions of lipid, protein, ash and water) and energydensity (ED; kJ g^-1) of prey, and their variability, are known poorly. In this study, key prey species from Newfoundland and Labrador were studied: Atlantic cod Gadus morhua, American plaice Hippoglossoides platessoides, sandlance Ammodytes dubius, Arctic cod Boreogadus saida, northern shrimp Pandalusborealis, redfish Sebastes spp., Greenland halibut Reinhardtius hippoglossoides, squid Illexillecebrosus and Gonatusfabricii, capelin Mallotus villosus, Atlantic herring Clupea harengus and daubed shanny Lumpenus maculatus. PC and ED varied greatly among species and were influenced by size, season, geography and year. Herring, capelin and G.fabricii had the highest ED, whereas Atlantic cod, plaice, sand lance and shrimp had the lowest. Halibut and I. illecebrosus increased in ED with size. EDs of capelin and redfish varied seasonally; that of plaice and sand lance did not. Herringand halibut had higher ED in the early 1990s than in recent years. Such variation in prey ED has important implications for digestive efficiency, foraging energetics, and dietary preferences of vertebrate predators.