The barren ground is an abnormal phenomenon of coastal ecosystem in which seaweeds, are destroyed and mostly replaced by the coralline algae containing the calcium carbonate components. To restore the seaweed forest, We have exerted an effort in the local areas, Samchuck, Korea, where barren phenomena are profound. Two methods of seaweed forest construction developed in the present study are underwater longline and seed transplantation for the brown seaweed Costaria costata, a fast growing edible seaweed. The sizes of C. costata attached on the underwater longline were $96.7{pm}2.2mm$ of blade length and $83.6{pm}7.7g$ of blade weight in April. Thereafter the sizes declined from May. Similar pattern was obtained from in the transplantation method with maxima of $90.4{pm}15.8mm$ and $70.1{pm}31.7g$ for blade length and weight, respectively in April. It appeared totality maturation from two methods in May. This maturation time is the same like that of wild C. costata.