Three isomers of yttrium carbide (Y2C2) endohedral metallofullerenes, i.e., (Y2C2)@C-82(I, II, III), have been synthesized and chromatographically isolated for the first time. The structures Of (Y2C2)@C-82(I, II, III) metallofullerenes have been characterized by C-13 NMR measurements, whose molecular symmetries have been determined to be C-s, C2(v), and C3(v), respectively. In addition, a pure diyttrium metallofullerene, Y-2@C-82(III), has also been synthesized and structurally characterized. The C-13 NMR structural analyses indicate that (Y2C2)@C-82(III) has exactly the same fullerene cage as that of Y-2@C-82(III). On the basis of the results, we propose a C-2-trapping and loss of growth mechanism of dimetallofullerenes Of (M2C2)@C-82 and M-2@C-82 from M-2@C-84,C- respectively.