The temporal-spatial distributions of SeaWiFS Chlorophyll a concentration(1998—2007)in the East China Sea waters(116?-135?E,21?-42?N)were analyzed by using Empirical Orthogonal Function(EOF)method.The first three dominant EOF modes were analyzed using power spectrum.For spatial variability,the climatological SeaWiFS Chlorophyll a shows that the concentrations of Chlorophyll a are high near coast and low offshore; for seasonal variability,the monthly climatological SeaWiFS Chlorophyll a is highest in spring(March-April)and lowest in summer(June-July).The first three modes of EOF contribute 84.89%,3.38%,and 1.06% of variation,respectively.The first mode accounts for most of the variability; the spatial distribution is consistent with the climatology mean;the time coefficients indicate that years 1998 and 2000 have lower Chlorophyll a than normal years,while year 2007 has higher Chlorophyll a than normal years; the linear fitting of Chlorophyll a concentrations shows a weakly positive trend.The second mode displays the seasonal variability with a significant period of 12 months using discrete power spectral analysis; the area near the Yangtse River Estuary,the Hangzhou Bay and along Zhejiang Province coast is positive and the other areas are negative.The time coefficients of the third mode show two significant periods of 12 months and 6 months; an area centered at 122.95?E,32.24?N are negative while the Yellow Sea and the area offshore Zhejiang Province are positive,which is probably related with the variability of along shore currents,expansion of the Changjiang River diluted water and Taiwan Warm Current.