The aim of this study is to analyze the accuracy of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) over Istanbul metropolitan city. Accuracy assessment was conducted by comparing ASTER GDEM with a reference DEM derived from 1/5.000-scaled topographic maps. The selected area has wide range of elevations since it covers coastal and mountainous areas. Different land cover types like urban, sea, lakes, agricultural land, forest, grasslands, bare lands are available within the study area. The accuracy assessment of GDEM was performed by visual interpretation and statistical analysis. Throughout the statistical analysis, several transects representing different types of land cover and topography were selected and minimum, maximum and mean errors and Root Mean Square Error values of each transect were calculated, respectively. The quality of ASTER GDEM was analyzed for Istanbul region and it was found that ASTER GDEM could represent the main topographic features of Istanbul precisely yet there are some erroneous representations over some parts of the study area. In most part of the study region, ASTER GDEM has 20 m or better accuracy however in some portions error values are higher than 20 m.