A study on the decontamination of dredged coastal sediment and its utilization for red-tide control were performed. The organic matter contained in the sediment could be stabilized aerobically, but the performance was affected by the content of soluble and degradable organics. For the sediment with high organic content of 2000 mg SCOD/L, the SCOD could be decreased to 400mg/L in the aerobic stabilization reactor with 5days HRT after the acclimation of 60days. In the case of the sediment with lower organic content (100-400mg SCOD/L), the stabilization efficiency was relatively lower than the sediment with higher SCOD. However, the stabilization of organic matter in the sediment could be enhanced by some pretreatments, such as alkaline (NaOH) treatment or ultrasonication, increasing the degradability of the organic matter. The heavy metals contained in sediment could be detoxified by the metal-phosphate immobilization with an ultrasonication, and the immobilization performance was affected by both the equivalent ratio of metal and phosphate and the ultrasonication (intensity, radiation time). The stabilized sediment was quite effective for the red-tide control in near shore coastal sea. When the sediment (diluted to proper concentration) was sprayed on the sea water surface, the sediment particles were quickly settled down to the bottom. During the settling, the tiny particles of the sediment was attached on the surface of the red-tide organisms, and swept out from the sea water. The effectiveness of sediment on the red-tide organisms could be described by a surface adsorption, a control failure of the osmotic pressure and an expansion and rupture of the cell wall, and the removal from the settling. It was concluded that the dredged sediment could be used as a good material for the red-tide control in coastal sea, if the pollutants including degradable organics and heavy metals were stabilized.