We processed 5.6 years of TOPEX/Poseidon altimeter data and obtained time series of sea level anomaly (SLA) over the South China Sea (SCS). Fourier analysis shows that sea level variability of the SCS contains major components with periods larger than 180 days and is dominated by the annual and semiannual components. Tidal aliasing creates 30--180 day components that can be misinterpreted as wind-induced variabilities. Continuous and multiresolution wavelet analyses show that the SLA of the SCS has monthly to interannual components of time-varying amplitudes, and the regional slope of SLA is 8.9 mm yr-1, which may be caused by the decadal climate change. Coherences of SLA with wind stress anomalies (WSA) and sea surface temperature anomalies (STA) are significant at the annual and semi-annual components. At periods of 2--5 years the wavelet coefficients of SLA, WSA, and STA have the same pattern, but WSA leads SLA, and STA follows SLA. The zero crossing of SLA in spring is highly correlated with the onset of the summer monsoon. The interannual variability of SLA is correlated with El Ni¿o-Southern Oscillation, and most important is that when the El Ni¿o-like wavelet coefficients of SLA over the warm pool northeast of Australia or the SCS change curvature from negative to positive, an El Ni¿o is likely to develop. This is a contribution to the South China Sea Monsoon Experiment (SCSMEX). ¿ 2000 American Geophysical Union