The objective of this research was to study the effect of pre-coagulation on the removal of colloidal particles by applying membrane filtration. In this research, colloidal silica solutions were coagulated with Fe3+ first to increase the particle size, and then filtered through PVDF membrane by applying the dead-end filtration process. Deviations from the conventional cake filtration theory in the plot of dt/dv vs. v are shown again and none of the above theories can explain this phenomenon successfully. By using the critical- flux hypothesis and cake erosion term in conventional dead-end cake filtration theory, a theoretically sound model is introduced to simulate the flux decline successfully in this paper. Includes 16 references, figures.