This study focuses on the coagulation mechanism by the purified coagulant solution (MOC-SC-PC) with the coagulation active component extracted from M. oleifera seeds using salt solution. The addition of MOC-SC-PC into tap water formed insoluble matters. The formation was responsible for kaolin coagulation. On the other hand, insoluble matters were not formed when the MOC-SC-PC was added into distilled water. The formation was affected by Ca2+ or other bivalent cations which may connect each molecule of the coagulation active component in MOC-SC-PC and form netlike structure. The coagulation mechanism of MOC-SC-PC seemed to be an enmeshment by the insoluble matters with netlike structure. In case of Ca2+ ion (bivalent cations), at least 0.2mM was necessary for coagulation at 0.3 mg-C l-1 dose of MOC-SC-PC. Other coagulation mechanisms like compression of double layer, interparticle bridging or charge neutralization were not responsible for the coagulation by MOC-SC-PC.