Regioselective bisaddition of M3N@I-h-C-80 (M = Y, Gd) was observed for the first time in the Prato reaction with N-ethylglycine and formaldehyde. The main kinetic bisadduct of Y3N@C-80 was determined to be a [6,6],[6,6] adduct by H-1 and C-13 NMR and vis/NIR spectroscopy, and it converted to a mixture of regioisomers upon heating via a sigmatropic rearrangement. The main kinetic bisadduct of Gd3N@C-80 (the [6,6],[6,6] adduct on the basis of vis/NIR data) existed stably under thermal conditions without isomerization. The likely position of the second addition of the Gd3N@C-80 bisadduct was predicted by DFT calculations.