The instrument level ground test of the Geostationary Ocean Color Imager(GOCI) has been completed and integratedonto the Communication, Ocean and Meteorological Satellite(COMS) which is scheduled for launch in late 2009.In order to monitor the short-term biophysical phenomena with better temporal and spatial resolution, The GOCI hasdeveloped with eight VNIR bands, 500m GSD, and 2500km×2500km coverage centered at 36N and 130E. The GOCIplanned to observe the full coverage region by every hour in daytime, and provide 8 images in daytime during single day.The GOCI ground test campaign for characterization and calibration has been performed by Korea Aerospace ResearchInstitute(KARI), Korea and EADS Astrium, France. Korea Ocean Research & Development Institute(KORDI) hasverified that test results satisfy all the GOCI performance requirements(Ex. MTF, SNR, Polarization, etc.) requested byKORDI.The GOCI has been sufficiently characterized under both of ambient and thermal-vacuum environments in order todevelop the on-orbit radiometric calibration algorithm. GOCI radiometric model has been finalized with 3rd orderpolynomial. Because solar calibration is the on-orbit radiometric calibration method of the GOCI, Solar Diffuser madeof fused silica and Diffuser Aging Monitoring Device(DAMD) are implemented as on-board calibration system.Diffusion factor of the Solar Diffuser and DAMD with respect to the solar incident angle, wavelength, and pixel locationhas been successfully characterized. Diffuser aging factor has been calculated for the compensation of the diffuserdegradation by space environment. Diffusion factor of Solar Diffuser and DAMD, and diffuser aging factorcharacterized during prelaunch ground test are implemented into the GOCI radiometric calibration S/W developed by KORDI.