Sludge cakes sampled at various positions and times in an electroosmosis-dewatering chamber were analyzed using microtome-slicing techniques. The flocs accumulated at the anode due to the electrostatic attraction. The porosity continued to decrease as most of the biomass coagulated into large clusters. During the constant-rate period of moisture removal, the morphological differences between the cakes at the two electrodes were less significant. During the falling-rate period, a relatively large difference in cake porosity appeared between the electrodes, involving difference in pore size, porosity, Sierpinski fractal dimension (D-SC), and pore boundary fractal dimensions (D-B).