Dietary studies are critical to an understanding of elasmobranch ecology and the role they play in marine ecosystems. The stomach contents of 136 male and 100 female Heterodontus portusjacksoni were obtained from July 2004 to March 2005 near Newcastle, New South Wales. The diet was broad (41 prey taxa) and displayed clear ontogenetic differences, but no differences between the sexes. Juveniles consumed mostly benthic infauna and epifauna (eg. Echiuroidea), whilst subadults occupied a transitional position to the adult diet, which was dominated by demersal pelagic prey (eg. squid). An ontogenetic shift in trophic level from secondary consumers (juveniles- subadults) to tertiary consumers (adults) in combination with the change in dietary composition, indicates a maturity-related shift in the ecological role of this species. Although some dietary overlap occurred, the ontogenetic variation in diet clearly demonstrated intraspecific resource partitioning was operating during the time that the three maturity stages cohabited.