Recent advances of medaka bone development are described, which include osteoblast- and osteoclast-specific cells and marker genes, by using new techniques: screening of medaka bone and fin ray mutants followed by positional cloning, and transgenic lines employing osteoblast and osteoclast specific promoters linked with a fluorescent protein, in addition to electron microscopy for histology. Because live imaging becomes the most powerful tool for characterization of cell development and organ formation, studies of bone development in medaka as an animal model bring new molecular and cellular insights of bone by visual data from the medaka line specifically derived from coupling the transgenic line with a mutant.