Seaweed biomass was estimated in the rocky subtidal zone of Daejin on the mid-east coast of Korea using a destructive sampling method from February to November 2007. Monthly sampling was conducted at depths of 5, 10 and 15 m using 50 $ imes$ 50 cm quadrats. A total of 73 species, including 5 chlorophytes, 25 phaeophytes, 43 rhodophytes and one seagrass were identified. Average seaweed biomass was 2,852.3 g wet wt. $m^{-2}$ and biomass values varied monthly from 1,189.8 g to 7,523.7 g. The species dominant in biomass were Laminaria japonica (481.7 g), Sargassum confusum (470.85 g), Undaria pinnatifida (422.57 g), Costaria costata (282.16 g), Odonthalia corymbifera (174.46 g), S. sagamianum (163.22 g) and S. horneri (122.18 g). The vertical distribution of algae was characterized by S. confusum and U. pinnatifida at 5 m, L. japonica and U. pinnatifida at 10 m, and O. corymbifera and L. japonica at 15 m depth. The C/P, R/P and (R+C)/P values were 0.20, 1.72 and 1.92, respectively.