The equilibrium geometries of three isomeric hexapyrrolidine C-60 adducts with T-h, D-3, and S-6 symmetries are optimized by means of the B3LYP method at the 6-31G* basis sets in this paper. On the basis of the optimized structures, the excited state and third-order nonlinear optical properties, such as third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG), and degenerate four-wave mixing (DFWM), and two-photon absorption (TPA) cross sections, delta, are calculated by using the TDB3LYP model based on the 6-31G* level coupled with the sum-over-states (SOS) method. The computational results show that the transition energies from S-0 to S-1 of the T-h hexaadduct and the D-3 hexaadduct have a remarkable blue shift by comparison with that of the C-60 parent. These results are in agreement with experimental ones. However, the first singlet excitation energy of the S-6 hexaadduct has a red shift compared with that of the C60 parent. Accordingly, we predict that different positions located by six addends may result in the different spectrum properties. Finally, the two-photon absorption cross sections indicate that the largest average value of resonant TPA, , of the D-3 hexaadduct has a red shift compared with those of the T-h and S-6 hexaadducts.