MicroRNAs (miRNAs) refer to a category of small non-coding RNAs that down-regulate gene expression by binding to target mRNA for degradation or translational repression, and play important roles in differentiation, development, homeostasis, cell proliferation, apoptosis and metabolism.Few studies on miR-ls roles in the Japanese flonder(paralichthys olivaceus) development and its targets have been reported so far.The bioinformatic analysis indicated that one of miR-ls putative targets is HDAC4, a known gene related to transcriptional repressor of muscle gene expression.Despite some of genes have been predicted to be miRNA targets by bioinformatic analysis during Japanese flonder development, few of them have been verified by experiment.The objective of our study is to identify the miRNAs targeting HDAC4.We initially cloned the 3UTR of HDAC4 and analysised the putative miRNAs in the 3UTR.Among the predictive miRNAs,miR-1 is the miRNAs predicted by the three used websites.In our study, the results of luciferase reporter assay, realtime-PCR demonstrated that miR-1 directly targeted on the 3UTR of hdac4 and down-regulate the expression of HDAC4 at mRNA levels.Furthermore, TH stimulating assay showed that miR-1 promote the metamorphosis of flounder by targeting HDAC4 in part.In our research, we concluded that by targeting the HDAC4, miR-1 can be involved in the flounder development.