Provided is a polyhedral transition metal complex including a hollow shell, the hollow shell including n1 (where n1 is an integer from 6 to 60) transition metal atoms and 2(n1) bidentate organic ligands, the bidentate organic ligands including a group derived from a polyhydroxy compound via a linking group, and formed so that the group derived from the polyhydroxy compound is oriented toward an inner space of the hollow shell. Also provided are: an ultrafine particle-containing transition metal complex including the polyhedral transition metal complex, and ultrafine particles of a metal oxide, the ultrafine particles being included within the hollow shell of the polyhedral transition metal complex; a method of producing the same. The invention thus provides a polyhedral transition metal complex that makes it possible to efficiently produce metal oxide particles having a uniform particle size of several nanometers, an ultrafine particle-containing polyhedral transition metal complex in which metal oxide particles are included within a polyhedral structure and the method of producing the same.