The objective of this research was to study on the relationship between predator and prey for yellowfin tuna in Tomini Bay. Sampling site were located at Marisa, Gorontalo Province in 2007. Prey composition of yellowfin tuna was visually determined. The results showed that there was no relationship between the size of yellowfin tuna and their preys, however, there was indication that different size of yellowfin tuna feed on different item of foods. Adults yellowfin tuna feed little tuna (Auxis rochei) and small pelagic fish Brama dussumieri and Selar cromenopthalmus), while immature yellowfin tuna feed mostly Canthigaster spp., Monacanthidae and Balistidae.