The title compound, [Co(2)(O(2))(CH(3)CN)(2)(C(2)H(8)N(2))(4)](ClO(4))(4), consists of centrosymmetric binuclear cations and perchlorate anions. Two Co(III) atoms, which have a slightly distorted octa-hedral coordination, are connected through a peroxido bridge; the O-O distance is 1.476 (3) Å. Both acetonitrile ligands are situated in a trans position with respect to the O-O bridge. In the crystal, the complex cations are connected by N-H⋯O hydrogen bonds between ethyl-endiamine NH groups and O atoms from the perchlorate anions and peroxide O atoms.