Transparent Exopolymer Particles (TEP) is a sticky amorphous colloids ranging between μm- to mm-size and consisted mainly of acidic polysaccharides. Recently, the interesting substance, originating from phytoplankton and bacterioplankton in the nature water, was regarded as the major membrane biofouling initiator. TEP is a major agent in the aggregation of particles and easily accumulate on reverse osmosis membrane surface. As a result, it facilitates initial stage of biofilm formation and eventually become biofouling. This study firstly is aimed to investigate the fates and distributions of TEP in seawater desalination plants around Taiwan and on the outside islands based on the in-situ monitoring platform set up in the last project. Secondly, the effects of TEP with organics (e.g. humic and algnic acid) and ions (e.g. Ca, Mg, Boron) in the simulated seawater influent is tested the degrees of contributions on biofouling. Membrane properties, such as hydrophobicity, surface charge and roughness, are also investigated. Lastly, the effectiveness of pre-treatment and biocides on biofouling control are considered to demonstrate in the end of the study. The results are supposed to contribute to current constructing desalination plants in eliminating the die-hard biofoulants.