Hetero-binuclear superhalogen anions, namely MM'F-4(-) and MM '' F-5(-) (M = Li, Na; M' = Be, Mg, Ca; M '' = B, Al, Ga), have been theoretically characterized at the MP2(FULL)/6-311+G(3df) level. It is found that two central atoms can be linked by at most three fluorine ligands. The large vertical electron detachment energies (VDEs, 7.449-8.978 eV) verify the superhalogen identity of these anions. The VDEs of both MM'F-4(-) and MM '' F-5(-) decrease when the atomic size of M increases whereas increase with the size of M' and M ''. Besides, the extra electron distribution also has effect on the VDEs of such superhalogen anions. (C) 2017 Elsevier B.V. All rights reserved.