Thermal carbosilylation of endohedral dimetallofullerene La-2@I-h-C-80 with silirane (silacyclopropane) is reported herein for the first time. Two diastereomers of the carbosilylated La-2@I-h-C-80 have been isolated and characterized. The fascinating molecular structure of one diastereomer of the carbosilylated derivatives has been determined unambiguously using X-ray crystallographic analysis. Detailed characteristics of the molecular structures including their metal atom movements have also been revealed using NMR spectroscopic studies and computational calculations. Results revealed that two La atoms move dynamically inside the carbon sphere. Furthermore, electrochemical study has demonstrated that carbosilylation is effective to fine-tune the La-2@I-h-C-80 electronic properties.