The disposal of the dredged soil has recently become a worldwide problem. In order to utilize high water content soil material, it is essential to dewater and increase the soil strength. There are urgent demands for developing an alternative new method to dewater the dredged soils in more economical and environment-friendly viewpoint. In this paper, siphon method with porous filter material is proposed to dewater the high water content dredged soil. In order to clarify the availability and effectiveness of this method, a series of tests were performed to investigate the dewatering behavior and strength of the dredged soil with vacuum and siphon methods. It was found that there is some possibility to dewater the dredged soil by using siphon method with vertical pressure.