Digestion rate markedly increased as exonuclease Ⅲ digesting linear DNA with double chains which had reacted with Bleomycin A₅-Ce(Ⅲ) ［BLMA₅-Ce(Ⅲ)］. In additon, there were other products to the four mono-nucleotides (5-dAMP, 5-dTMP, 5-dCMP, 5-dGMP). It is suggested that BLMA₅-Ce(Ⅲ) cleaves phosphooryl diester bonds along the direction of 5′～3′ at specific sides of double-chain DNA forming more exposed 3′-OH ends.