The Marino Forum 21 started an R&D project in fiscal 2000 with grants from the Japanese Ministry of Agriculture, Forestry, and Fishery to develop the equipment for the eutrophication of the sea by upwelling deep ocean water, sending into euphotic zone and increasing phytoplankton. First, some concepts of moored floating structure with a riser pipe for deep ocean water upwelling at the water depth of 500m were investigated and evaluated by computer runs. Second, based on the investigation, basic design of the structure was undertaken. Next, scaled model tests were carried out in an experimental tank at several wave conditions in order to evaluate dynamic response of motion of the structure, mooring force and riser pipe stress. Finally, based on this experiment, possibility of the structure and validity of the computation were verified.