A particle size analyzer together with a video camera has been used to investigate the structure of the aggregates during the process of aggregation and breakup of particles in a shear flow induced by means of a Couette-flow system. Three different values for the shear rate have been used (25, 32, and 50 s(-1)). The initial volume fraction of the particles was phi(o) = 5.0 x 10(-5). Different fractal dimensions (D-3), D-2, D-1, and D-pf), the shape factor (xi(2)), and the aspect ratio (AR) have been used to characterize the structure of the aggregates. During the process of aggregation, no significant changes in the fractal dimensions, shape factor, and aspect ratio were found. The high values obtained for D-3 (D-3 = 2.2) and D-2 (D-2) = 1.98) show us the high compactness of the flocs. Also, values of the fractal dimension and shape factor have been found to not depend on the shear rate.