A total of 4181 stomachs of yellowfin tuna,Thunnus albacares (22–164 cm FL), mainly caught by gillnets in the period from July 1984 to June 1986 were analyzed. Food consumption of yellowfin tuna in nature was determined using the values of the average stomach content, incorporating laboratory measurements of gastric evacuation rates in a feeding model. The diet of yellowfin tuna around Sri Lanka comprised a variety of macro zooplanktonic and nektonic organisms. Juveniles < 39 cm FL, are planktivores. Tuna > 40 cm FL gradually increase their consumption of fishes with increasing size. Among fish speciesAuxis sp. are the most important. The daily food consumption of juvenile yellowfin tuna (22–59 cm FL) range from 1.8 g to 136.2 g, increasing to about 284.7 g to 551.9 g for the medium size tuna (60–99 cm FL). The adult tuna (100–>130 em FL) consume around 513 g to 538.8 g of prey per day. Daily ration estimates increase from 2.1% to 5.5% of body weight with increasing size up to 70 cm FL, beyond which it decreases. The predatory pressure of yellowfin tuna on commercially important fishes and other species is discussed.