For the first time, Th@T-d(19151)-C-76, a highly symmetric C-76 cage encapsulating an actinide metal ion, has been synthesized and characterized by single-crystal X-ray crystallography, mass spectrometry, UV-vis-NIR spectroscopy, and cyclic voltammetry. The single-crystal crystallographic analysis unambiguously assigned the fullerene cage as T-d(19151)-C-76 and confirmed Th@T-d(19151)-C-76 as the first IPR (isolated-pentagon rule) C-76-based monometallofullerene. The crystallographic results further revealed that the optimal Th site resides over a sumanene-type hexagon, similar to that of the Th@C-1(11)-C-86 but different from the previously reported Th@C-3v(8)-C-82. In addition, electrochemical study found that Th@T-d(19151)-C-76 processes an unusually low first oxidation potential (0.03 V), suggesting its strong electron donating ability.