When fed on one of the six isonitrogenous (45%) and isolipic (8%) feed containing 5 or 10% Undaria, 2% wasabi leaf, 2% wasabi stem and 0.5% herb (Obosan) for a period of 8 weeks, 95-98% juvenile flounder survived. Growth, feed efficiency and condition factor of the flounder fed on diet containing 0.5% herb were significantly (p<0.05) higher than those fed on diet supplemented with 10% Undaria. There was no significant (p>0.05) differences in moisture, crude protein, lipid and ash of the flounder receiving the different diets. The flounder fed on diet supplemented with 10% Undaria had the highest moisture but the lowest lipid in liver. Hematological parameters such as red blood cell, hematocrit and hemoglobin and serum constituents such as glucose, total cholesterol and glutamic-oxaloacetic transaminase of the flounder fed on the diets varied but no specific trend became apparent. Lysozyme activity in the serum of the flounder fed on diet supplemented with 5% Undaria and the herb, as well as nitroblue tetrazolium (NBT) reduction of macrophage in the head kidney of the flounder fed on diet containing the herb and 2% wasabi stem were significantly (p<0.05) higher than those receiving control diet. Briefly, the herb supplementation promoted growth and that of Undaria and wasabi stem enhanced non-specific immune response.