Restoration of a Sargassum forest was challenged at an enclosed block （10×10 m） on Diadema barren in Uchiura Bay, on the northwest coast of Izu Peninsula, Shizuoka Prefecture. In the block, Diadema was monthly removed and invasion of Diadema was prevented by deploying fences（ rolled gill nets）. To introduce a mass of Sargassum embryos, thalli of S. piluliferum were installed in the suspended net （ 1.5×3m ） laid at a height of 1 m from the bottom（ 4 m in depth） in April and May 2009 and May 2010. In 2009, transplanted thalli of S. piluliferum matured in June；hundreds of juveniles （less than 2cm in height） appeared in August. Although Diadema invaded the block and consumed most of the juveniles before deployment of the outer fences, 20 juveniles survived and grew rapidly on the cobbles covered with small macroalgae. The juveniles grew up to 60 cm in average （180 cm at maximum） in height in May 2010. Although the canopy disappeared in September, juveniles appeared in January. Monthly average of water temperature ranged between 13.7℃ in March and 24.5℃ in August in 2009. In 2010, however, transplanted thalli of S. piluliferum failed in maturation. The higher water temperature （from 14.2 in February to 27.8℃ in August） may inhibit its maturation.