When and how fledglings become independent are important issues in understanding the life history of long-lived seabirds. In this study, we investigated post-fledging care, development of foraging skills, and the ultimate causes of independence in juvenile Red-footed Boobies (Sula sula) on Dong Island, Xisha Archipelago, northern South China Sea, during 2007 and 2008. After fledging, juveniles took an average of 118 days to become independent; the post-fledging survival rate was 96%. Parents supplied the young with more food after they fledged (average 176 g day^-1) than before, but the mass fed per day declined significantly at the end of the post-fledging period. Juveniles' foraging trips lengthened progressively and probably served mainly to develop foraging skills, as 94% of their food was supplied by their parents. Juveniles foraged for themselves mostly from 60 days post-fledging onward, which was just adequate for survival at independence. Fledglings became independent when foraging was energetically more profitable than begging food from the parents, whereas parents significantly reduced the mass of food delivered to the fledgling when the fitness increment from another nesting exceeded that from attending their current young. Nonsystematic checking of the nest area showed that at least 60% of fledglings still survived 20 to 84 days after independence, indicating that the strategy for achieving independence is successful. This study is the first to analyze the independence ontogeny of a long-lived seabird quantitatively.