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We observed the morphological behavior of ABC mikto-arm terpolymer with a C₆₀ additive. ABC mikto-arm terpolymers, consisting of polystyrene, polyisoprene and poly(2-vinylpyridine) (PS-PI-P2VP), with various P2VP volume fractions were examined. The role of C₆₀ on the morphological behavior of mikto-arm terpolymer was studied by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The affinity of C₆₀ to PS or P2VP was examined by neutron reflectivity. C₆₀ can form charge-transfer complexes with electron donating pyridine groups in P2VP blocks. Before and after charge-transfer reaction, C₆₀ showed different effects on the self-assembly of mikto-arm polymers. The domain spacing, interfacial width, and morphology of mikto-arm terpolymers were changed depending on the concentration of C₆₀.