Quality evaluation of fish muscle was conducted in olive flounder, Paralichthys olivaceus fed with control or experimental diet containing 0.3% of Obosan (Sungam Co., Korea). Sensory panel members preferred the experimental fish were more preferable than those of control (P<0.01 or 0.05). The difference test was shown that the experimental fish muscle is more firm elastic and palatable than the control ones (P<0.01 or 0.05). The physical properties of meats from fish fed a diet containing Obosan improved qualities with compared to those of control meats. The total amount of free amino acids in muscles from control fish (31.7 mg/100mg), especially with the significant increase of glutamic acid, proline, glycine, alanine and methionine. In all nucleotides and their related compounds, ATP was the most abundant in muscles from fish fed a diet containing Obosan (about 1.9 fold compared to mean of control), however, IMP was more abundant in control muscles.