A new experimental method was developed to determine the porosity of cake layer formed during microfiltration of aggregates made from latex beads, and the dependence of porosity on fractal geometry of aggregate was studied. The cake layer was visualized by a confocal laser scanning microscope (CLSM) and then image analysis technique was applied to measure the porosity. Aggregates were made from fluorescent polystyrene latex beads under various conditions and then their sizes and fractal dimensions were measured. Each aggregate suspension was microfiltered to form a cake layer on the membrane surface. Experimental results showed that for the low range of fractal dimension the cake porosity may hardly depend on the fractal dimension of aggregates, but for the region of higher values it may decrease with increasing of the fractal dimension.