Visits were made to the Xisha Archipelago, northern South China Sea, from 13 March to 9 April 2003 and 2 April to 7 September 2004, to determine the status of the Red-footed Booby (Sula sula). The Red-footed Booby was found to breed only on Dong Island, (area of 1.55 km²). Random sampling indicated that the island supported approximately 35,500 breeding pairs. The colony is the largest in the west Pacific and comprises more than 10% of the estimated world population. It is suggested that the island may hold more than 100,000 individuals, including fledged birds of the year, and immature and non-breeding birds. The Red-footed Booby nests only in Pisonia grandis trees on the island, and the most serious threat to the breeding colony is from a herd of introduced cows which are consuming the new P. grandis growth that otherwise would develop into potential nesting habitat. Recommendations are made for improved protection of birds on the Archipelago.