Based on ten ocean color images that were obtained simultaneously by the Ocean Color Imager (OCI) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), an intercomparison study shows that the two data sets are highly correlated. The data from the two different sensors were processed with SeaWiFS atmospheric correction and bio-optical algorithms to derive the chlorophyll-a concentration (Chl-a). The difference of total radiance received at the sensor of OCI and SeaWiFS is in the range of 3.8% at 510 nm to 21.5% at 865 nm. The difference of Chl-a derived from OCI and SeaWiFS is about 12.4%. Correlation coefficients between OCI and SeaWiFS of total radiance and Chl-a are higher than 0.91. The validity of the free data from OCI on-board ROCSAT-1, the first scientific experimental satellite of Taiwan, is established. ¿ 2001 American Geophysical Union