Objective：To explore the role and mechanism of miR-155 overexpression in the development of zebrafish embryos. Methods：The expression of miR-155 during each stage of embryogenesis was detected by quantitative RT-PCR. miR-155 mimic was microinjected to the 4 blastomeres of 4-cell stage embyos to overexpress the gene. The expressions of developmental related marker genes were detected by quantitative RT-PCR，and ETS1 mRNA was used to rescue embryos after overexpression of miR-155. Results：The expression of miR-155 was found in the whole embryonic development period and obviously increased in the periods of organogenesis. Overexpression of miR-155 leads to retardation of embryo development，delayed membrane depletion，abdominal and pericardial effusion，tail shortening and thickening，and down regulated the expression of genes related to liver，intestine，heart and muscle development. ETS1 can reduce the developmental malformation caused by overexpression of miR-155. Conclusion：Overexpression of miR-155 may affect embryonic development of zebrafish through negative regulation of ETS1.