Objective Gene knock-out animal is a species of experiment animal which can let people research gene function at individual level. It is based on the gene knock-out technique and embryonic stem cells. Now, it is widely used in many fields of life science research. The gene knock-out technique can not be replaced by RNA interference technique which grew over the last few years. The study and application of gene knock-out animal were reviewed in this article. Comparison between gene knock-out technique and RNA interference technique was also overviewed.