GOCI, the first Geostationary Ocean Color Imager, shall be operated in a staring-frame capture mode onboard its Communication Ocean and Meteorological Satellite and tentatively scheduled for launch in 2008. The mission concept includes eight visible-to-near-infrared bands, 0.5km pixel resolution, and a coverage region of 2500 2500km centered at 36N and 130E. The instrument measured the solar reflected radiation in eight spectral bands in the visible and near-infrared parts of the spectrum has had the scope of its objectives broadened to understand the role of the oceans and ocean productivity in the climate system, biogeochemical variables, geological and biological response to physical dynamics and to detect and monitor toxic algal blooms of notable extension and hazardous materials, such as oil spills through observations of ocean color. The instrument is expected to provide SeaWiFS quality observations with the frequencies in acquisition of the imagery 8 times during daytime and 2 times during nighttime. The ocean color imager shall have a special feature to enable imaging any portion of the globe. In order to achieve the goal of the mission, the different radiometric and geometric requirements have been refined by taking into account the constraints imposed by a geo-orbiting platform and the technical capabilities of the imager. Since being the geo-orbiting platform and a wide aerial coverage, the mode of operation of the instrument remains a challenging issue and shall be finalized in the forthcoming RFP. Korea Aerospace Research Institute (KARI) and Korea Ocean Research and Development Institute are coordinating sensor characterization, design and performance. The GOCI shall be expected to complement measurements of ocean color with the high spatial, spectral, temporal and radiometric resolutions.