A purification effect for polluted water by a difference of an immobilization supports was studied using a microbial membrane bioreactor system. This system consisted of two types of bioreactors to immobilize anaerobic and aerobic microorganism. The river water of high degree of pollution was examined by this system. In this study, a porous sintered material was used for an anaerobic reactor. For water purification, two types of urethane (AQ-3, AQ-4) and a porous sinstered material were examined for adequacy as an immobilization support for aerobic reactors. By exchanging one type of support by another type, a purification effect was examined in terms of BOD, COD, TP (total phosphorus) and TN (total nitrogen). The purification effect of the porous sintered material and that of AQ-3 or expensive urethane of high vesicularity were more or less on the same level while the purification effect of AQ-4 or urethane of low vesicularity was on a level lower than the other two supports. In terms of maintenance of the system, AQ-3 was considered the best as an immobilization support. The purification efficiency of AQ-3 in optimal operating conditions was BOD 92%, COD 64%, TP 38%, and TN 34%. In conclusion, when installed in the home drainpipe, this system would be quite effective for purifying domestic wasted water.