The CRISPR /Cas system identified in archaea has been adopted and optimized for genome editing purposes in zebrafish. In vitro transcribed guide RNA and Cas9 mRNA are microinjected into fertilized zebrafish embryos to edit the zebrafish genome. Here, we describe how to design a gRNA, a fast method for in vitro transcription of gRNA from oligonucleotides , microinjection into fertilized zebrafish embryos, and a PCR -based restriction fragment length assay to identify mutations at the gRNA target site.