We report that the thermally activated conductivity in several fullerene systems obeys the Meyer–Nelder (MN) rule, σ = σ00eΔE/kT0e−ΔE/kT. We found that the MN conductivity σ00 and the characteristic energy kT0 have a strong correlation, which is in good agreement with the prediction of the model proposed by Crandall [R. S. Crandall, Phys. Rev. B 43, 4057 (1991)] and Chen [Y. F. Chen and S. F. Huang, Phys. Rev. B 44, 13 775 (1991)]. In this model, the origin of the MN rule is attributed to the exponential energy distribution of the defect traps. A similar correlation between σ00 and kT0 is also found in chalcogenide glasses. © 1998 American Institute of Physics.