Bacteriolytic mechanisms of Cu²⁺ ion solutions on the bacterial cell walls and DNA base-pairing damages were considered on the basis of the bacteriostatic and bactericidal actions resulting from the antimicrobial susceptibility tests, using Cu ion complex formations and producing reactive oxygen species (ROS). Bacteriolysis of Cu^2＋ ion solution against S.aureus cell wall was composed of the damages of PGN synthesis enzymes TG, TP due to the reactions of the polymerization of glycan chains and the cross-linking of peptide chains, and the activations of PGN forth autolysins. The other, bacteriolysis of Cu²⁺ ion solution against E.coli cell wall occurred by the destruction of outer membrane structure. The bacteriolytic actions consisted of the degradation of outer membrane lipoproteins at N- and C-terminals, and of the inhibitions of PGN elongation due to the deletions of PGN-TP enzyme and PGN autolysins. Reactive oxygen species (ROS O₂⁻, H₂O₂, ･OH) formed by Cu ion penetration into the cell walls may be influenced to the antibacterial activities. DNA base-pairing damages had occurred by Cu²⁺ substitution into hydrogen bonds in base-pairing G:C, A:T pairs.