An erbium (III) complex of a pentadentate Schiff base ligand [(NO3)Er(μ-L)2Er(NO3)].2H2O [H2L=bis( N-salicylidene)-3-oxapentane-1,5-diamine] has been synthesised, characterised and its structure confirmed by X-ray crystallography. H2L and the Er(III) complex both bind to DNA via a groove binding mode, and the Er(III) complex binds to DNA more strongly than H2L. The complex shows strong scavenging effects for hydroxyl radicals (OH·) and superoxide radicals (O2-).