Due to the enormous increase in nanopowder production, it becomes necessary to find and develop adapted characterization techniques. In the case of nanostructured agglomerates, the structure of these particles has a direct impact on flowing, and handling, but also on end-use final product properties. In this work, a fractal approach is used to characterize the agglomerate structure using two different, commercially available and widely used, methods: static light scattering (SLS) and image analysis of scanning electron microscope (SEM) photographs of the aggregates. Fumed silica aggregates are used for this comparison. The results by image analysis show that fumed silica aggregates have a two-level structure, made of compact aggregates of open aggregates of nanoparticles. This structure is not detected by SLS. For such a structure, SLS seems to be less accurate than image analysis method, although it could be an interesting technique in more simple cases, since it is a much less time-consuming technique. (C) 2010 Elsevier B.V. All rights reserved.