Abstract: The recent reseach developments of materials preparation, crystal structure, and especially thermoelectric properties of type -Ⅰ Ge clathrates are reviewed. Semiconducting type-Ⅰ Ge clathrates are thermoelectric materials that exhibit "phonon glass, electron crystal" （PC-EC） behavior. They have cage -like structure which leads to their good electrical properties, meanwhile, their thermal conductivity can be markedly reduced via filling alkaline earth or lanthanon into their cades, therefore, they are promising materials for thermoelectric applications. It is suggested that both the filling atoms and the framework atoms must be optimized in order to further improve the thermoelectric properties.