We study the electronic structure of decamethyl C-60 under an external electric field by investigating the radical spin arrangement using density functional theory. We find that antiparallel spin coupling (singlet state) is enhanced compared with parallel spin coupling (triplet state) by applying an electric field normal to the two isolated pentagonal rings surrounded by methyl groups. Furthermore, the electric field is found to change the relative stabilities of the spin states, leading to the possibility of spin state modulation of decamethyl C-60 by an electric field. (C) 2014 Elsevier B.V. All rights reserved.