The Luzon Strait transport, as an index for the South China Sea throughflow, has attracted much attention recently. In this study the interannual variability of Luzon Strait transport is examined, using the Island Rule and results from ocean data assimilation. Transport variability obtained from these two approaches is consistent with each other. Assessment of contribution from each integral segment involved in the Island Rule indicates that wind stress in the western and central equatorial Pacific is the key factor regulating the interannual variability of the Luzon Strait transport, whereas the effect of local wind stress in the vicinity of the Luzon Strait is secondary. Analysis also shows that when the westerly (easterly) wind anomalies in the tropical Pacific break out, the Luzon Strait transport increases (decreases), associated with the variations in the North Equatorial Current during El Ni¿o (La Ni¿a) events.