Histone deacetylase (HDACs) can control cell proliferation and differentiation by regulating the chromatin structure and inhibiting the activity of specific transcription factor.In view of the function HDAC1 played in the process of metamorphosis of tadpole, the expression of HDAC1 during metamorphosis of Japanese flounder (Paralichthys olivaceus) was investigated in this study.The full-length cDNA of HDAC1 gene with 2 540 bp was obtained from P.olivaceus, containing 126 bp-length 5'UTR, 1 470 bp-length ORF, and 944 bp-length 3' UTR.Expression of HDAC1 in coronary dorsal fin is gradually enhanced with the growth of coronary dorsal fin.Its expression on the fin fold was first found from 9 days after hatching (DAH), and later in 18 DAH larvae, mainly was found in the base of fin fold.The gene expression of HDAC1 in intestine increased with the intestinal being shorter and thicker.Then, it began to weaken at 16 DAH and eventually disappeared.The difference of HDAC1 expression between P.olivaceus and tadpole is its expression throughout the process of metamorphosis while only before metamorphosis in tadpole as reported in previous study.During the metamorphosis of P.olivaceus, HDAC1 gene was mainly expressed in pterygiophore, gill and skin around eyes.It expressed higher at the early stages of metamorphosis than later stages.The expression pattern of HDAC1 before and during the process of metamorphosis in P.olivaceus indicates it participating in the development of coronary dorsal fin and intestine, as well as the eye migration during metamorphosis.