Behavior of permeate flux decline was examined through the hollow fiber membrane in ultrafiltration system for Si colloidal solution. Flux decline with time was due to the growth of Si cake deposited on the membrane surface and the pore blocking by Si particles for the hollow fiber membrane. At the pseudo steady state of operation, the permeate flux of dead-end flow was 60% to that of the cross flow. The ratio of permeate flux to the pure water flux, J/Jw, decreased with increasing the trans-membrane pressure, from 64.2% for 0.5 kgf/cm(2) to 45.7 % for 2.0 kgf/cm(2). When the feed flow rate was 3 L/min, the pore blocking model was dominant at the initial period of filtration and was followed by the cake filtration model. And with increasing the feed flow rate from 1 L/min to 3 L/min, Rc was 1.79×10(12)~2.34×10(12) m(-1) which was the about 40% decreased value to that of the 1 L/min while Rp was not changed and was 1.71×10(12) m(-1) approximately.