Gene mutation is an important inducer for many diseases. With CRISPR/Cas9 system, it becomes possible to correct the mutated site in living cells. This technique is based on two factors, guide RNA and Cas9 nuclease. Guide RNA alters its sequence for different target sites, while Cas9 functions as a nuclease cutting double strand DNA. At the presence of template, homology directed repair pathway is activated for reconstructing the target site. Due to its versatility, CRISPR system is widely used all over the world and promotes the development of many research fields.