Understanding of chemical behaviour of actinide elements is essential for the effective management and use of actinide materials. The hollow internal cavity of fullerene buckyballs has been known to be able to encapsulate novel metallic units, especially those otherwise very reactive or virtually impossible to prepare clusters. In this talk, we will present our recent studies of novel actinide endohedral fullerenes, focusing on their unique bonding behaviors. We report the succesful synthesis and charaterization of UCN@C_s(6)-C₈₂, in which the UCN cluster demonstrates an unprecedented h²(side-on) coordination of U by a cyanide. The bonding analysis shows significant donation bonding between CN^- and uranium, and covalent interactions between uranium and the carbon cage, which results a rare case where the oxidation state of uranium shows ambiguity between U(III) and U(I). In addition, an unprecedented strong covalent Th-Th bondformed between two rarely accessible Th³⁺ ions, stabilized inside a fullerene cage nanocontainer as Th₂@I_h(7)-C₈₀. Both experimental and quantum-chemical results show that the two Th atoms have formal charges of +3 and confirm the presence of a strong covalent Th-Th bond inside I_h(7)-C₈₀. This work demonstrates the authenticity of covalent actinide metal-metal bonds in a stable compound and deepens our fundamental understanding of f element metal bonds.