A tank-submerged type membrane filtration system was developed for filtering highly turbid influent of water purification plants. Testing of microfiltration hollow fiber modules of this system revealed that a housing-less, sheet type module was most effective for the removal of suspended matter. Stable operation was enabled by the use of this module, with no rise in the transmembrane pressure difference during the inflow of highly turbid influent water. Test results indicated that this system was capable of long-term, continuous operation, without any influence by the quality of raw water. Solids entrapped in the filter media were able to be removed by air scrubbing only, therefore making backwashing unnecessary.