This thesis studied the changes in size and structure of particles subjected to different coagulation conditions using a small angle light scattering technique. The particles collected from Beishi River, Nanshi River and Shindian River and those prepared artificially were tested. Experimental results revealed that the origin of raw water nature affected significantly the aggregation dynamics of particles. Addition of organic matters with positive surface charge enhanced coagulation and produced compact aggregates. Various organic matters produced distinct interior structures of the PACl- clay pellets.