Cake resistance is influenced by floc size deposited on membrane surface. Enlarging floc size can reduce cake resistance. The small particles are enlarged by coagulation and flocculation processes in conventional mixing tank at membrane filtration system. Fully-grown flocs for reducing the cake resistance, however, are ruptured while passing through a pump. In light of this fact, this study aims to experimentally look at the reaggregation phenomenon through control of G-values in pipe from pump to inlet of membrane. in addition, reaggregation phenomenon of the mixing system is compared with first-aggregation in-line injection system in which coagulant is injected just before a pump. These results suggest that first-aggregation of in-line injection system is better than reaggregation of mixing system for G-value above 3100 s(-1). G-values in pipe of real world membrane filtration system are usually much larger than 3100 s(-1). Due to reason. in-line injection system is expected to perform better than mixing tank as proved in this study. (C) 2009 Elsevier B.V. All rights reserved.