Cloud macrophysical and microphysical properties derived from the NASA TERRA (EOS-AM) Moderate Resolution Spectroradiometer (MODIS) as part of the Clouds and the Earth's Radiant Energy System (CERES) project during November 2000-June 2001 are compared to simultaneous ground-based observations. The ground-based data taken by the Atmospheric Radiation Measurement (ARM) Program are used as "ground truth" data set in the validation of the CERES cloud products and to improve the CERES daytime and nighttime cloud retrieval algorithms. The datasets taken over the Southern Great Plains (SGP) site were used for this study. The CERES cloud products include effective cloud height and temperature, cloud-droplet effective radius, optical depth, and LWP/IWP. The CERES cloud products were averaged in a 30-km x 30-km spatial resolution centered on the ARM SGP site, while the surface data were averaged over an hour centered at the time of the TERRA overpass. There are totally 57 cloudy samples for daytime and 65 cloudy samples for nighttime in this study. Only those radar scenes that are classified almost entirely as either single layer cirrus or low-level stratus clouds are used in the comparison of cloud microphysical properties. The preliminary study shows that both daytime and nighttime CERES/MODIS cloud height, temperature, and microphysical properties agree fairly well with surface measurements and retrievals.