The waters surrounding Taiwan have a plenty of juvenile yellowfin tuna. The use of those fish as seeds for marine cage culture has drawn a great attention in Taiwan in recent years. Studies on size composition, condition factor and length-weight relationship of the fish caught from the coastal waters of Southern Taiwan were conducted. A short-term cage farming experiment, in order to explore sustainable tuna farming model, was carried out. Mean fork length and body weight and condition factor of fish caught from Xiaoliuque were 43.9 ± 8.2 cm, 1.5 ± 1.2 kg and 1.64 ± 0.13, respectively. On the other hand, mean fork length, body weight and condition factor of fish caught from Green Island were 79.8 ± 18.8 cm, 10.3 ± 5.9 kg and 1.73 ± 0.17, respectively. The specific growth rate (SGR) of a short-term cage cultured juveniles (about 100 days) was between 0.43 and 0.62%, the body weight gain (WG) was between 1 and 1.7 kg, and the average increase in the feed efficiency (FE) was 8.18%. The fork length increased 0.71 mm daily, the individual weight increased 0.49 kg per month, and the lipid content increased 4-18 times. The results showed that juvenile yellowfin tuna caught in the wild could increase in fatness and lipid content and its value after a short-term period of cage culture. The findings of this study could be helpful for the management of juvenile tuna resources and provide basic data for the tuna farming industry.