We report the synthesis, isolation, and characterizations of the novel trimetallofullerene Sm-3@I-h-C-80. Importantly, the experimental X-ray structure of Sm-3@I-h-C-80 verified for the first time that three metal atoms can be stabilized in a fullerene cage without a nonmetal mediator. Furthermore, computational studies demonstrated the electronic features of Sm-3@I-h-C-80, which are similar to that of theoretically studied Y-3@I-h-C-80. Electrochemical studies of Sm-3@I-h-C-80 showed a major difference from those of the well-studied isoelectronic species Sc3N@I-h-C-80 and La-2@I-h-C-80.