The structure of solid aggregates was investigated by using three particle analyzers; an electrical sensing zone, laser light diffraction and electron microscopy. Four particulate materials; aluminum trihydrate, aluminum phosphate, fly ash and iron hydroxide were used for the analysis of particle shape, size and floc structure. One of the primary conclusions of this work is that the floc structure could be characterized by the evaluation of the fractal dimension based on the experimental relationship between floc size and floc density through the free-settling test. It revealed that coarser flocs had a looser structure with a low value of fractal dimension.