An approach to DEM fusion was developed to improve the overall accuracy of DEMs and applied to two public products: Shuttle Radar Topographic Mission (SRTM) DEM and Advanced Spaceborne Thermal Emission and Reflection (ASTER) DEM. The relative ASTER DEM was co-registered to the SRTM coordinates and converted to the near absolute DEM by shifting the histogram to the average elevation of the SRTM DEM. The voids in one DEM were then filled through interpolation using the slope and aspect from the other DEM and using the elevation of surrounding pixels. Finally, the higher frequency components of the Optical DEM and the lower frequency components of the InSAR DEMs were filtered out, as they are more erroneous respectively. The filtered DEMs were then combined to generate the fused DEM. This approach was tested in a 6000 ha test site with fairly complex topography located in the central region of Nepal. The fused DEM shows up to 45% improvement in the accuracy measures like standard deviation and range of the errors. The approach showed promise to improve DEM accuracy and completeness while maintaining the resolution to the best of the participating DEMs. This approach increases the reliability and applicability of free and commercial DEMs produced by Optical and SAR remote sensing technologies.