Effective alginate extraction from waste-brown seaweeds was studied. The waste-brown seaweeds almost consist of stems of seaweeds. Alginate could be obtained from the stems as well as leaves of seaweed. Ultrasonic vibration(47kHz) facilitated filtering step in the alginate extraction process. Among various alkalies for alginate extraction, NaHCO3 was most appropriate concerning use of dealginates. The yield of alginate extraction using NaHCO3 2wt% solution was 19.3% at 60℃. The dealginates from NaHCO3-extraction process have been found most suitable food for red-worms.