Abstract: Discrete landscape characterizations with raster-based Digital Elevation Models (DEM) are commonly used for representing elevation surface in watershed modeling. As different resolution of elevation models could be available, this study investigates the impact of DEM resolution on a set of important topographic attributes and simulated runoff and sediment of the Zanjanrood watershed in northwest of Iran. Fifteen DEM realizations of different mesh sizes ranging from 10 to 500 m were used for comparative examinations. Models with different DEM resolutions were created in the SWAT model. The model was calibrated for flow and sediment yield using 10 m DEM data. The predicted output at the calibrated scale was used to evaluate output accuracy for the remaining input resolutions. Results of this study showed that DEM resolution affects the watershed delineation and all the terrain variables tested vary with the grid size change. It is found that the mean reach depth, mean elevations, mean slopes and the cumulated lengths of sub-basins and stream network, decrease as DEMs are aggregated progressively to coarser resolutions. As shown in this study a decrease in DEM resolution resulted in decreased runoff and sediment. The RE (%) variations of the yearly runoff and sediment loads due to resampled resolutions from 10 to 500 m were 1 and 11%, respectively. The decrease of the predicted sediment presents a nonlinear relationship with the DEM resolutions. Decreasing the resolution above 50 m did not substantially affect the simulation of runoff but it did have an impact on simulation of sediment yield.