Surface albedo is the ratio of the reflected solar radiation to the total amount that incidents on that surface. Urban albedo highly depends on surface geometric and physical properties, and thus has little uniformity. It is important to give realistic albedo values in urban modeling. With an emphasis on global scale urban regions, an analysis of 4-year bi-weekly MODIS albedo revealed that the albedos are typically lower in urbanized areas than the country counterparts, a direct result of the use of materials such as asphalt roadways and dark asphalt shingles on rooftops. Furthermore, urban albedo has evident seasonality as function of local solar zenith angle, with peak in July and minimum in January. The NCAR single column atmosphere-land surface model (CAM2/CLM2) proves that the reduction of urban albedo, typically about 5-10%, traps more radiation at surface and is the main reason for the urban heat island effect.