As an innovative method for embryo cryopreservation, vitrification not only reduced the cooling stage duration to a minimum, but also eliminated any injuries cased by extracellular ice, which is a major cause of cell injury. Therefore, if embryos are treated adequately, high survival can be obtained. As a component of a vitrification solution, a permeating cryoprotective agent is essential, and additional inclusion of a macromolecule and a small saccharide makes the solution more effective. The author's group composed a solution, designated EFS40, with ethylene glycol, Ficoll, and sucrose. This solution proved effective for the cryopreservation of various stages of embryos in many species. In this article, the author describes the detailed procedure for the vitrification of mouse morulae; related information is also described.