Nuclear transplantation technique is known as the most potential and efficient method for producing a large number of genetically identical animals from a single embryo. The technical development of nuclear transplantation in mammals and its application to the production of cloned animals are described. For the efficient and successful production of cloned embryos by nuclear transplantation, the right selection and micromanipulation of recipient eggs or embryos as capacious recipient cytoplasm, the adequate and benefitlal preparation of multiple totipotent embryonic cells as donor nuclei, and also the fusion technique are very critical. Recent studies approaching to these critical points are introduced and discussed. Up to date, the overall efficiency of production of cloned embryos and offspring in livestock is estimated to be low. Further technical development of nuclear transplantation will enable large-scale production of cloned livestock and in near future the commercial cloning of animals will become a reality.