Co-polymeric materials of Poly(Ethylene-Co-Vinyl Alcohol) with different ratios, P (EVOH), were chemically modified through a series of reactions including chloroacetylation followed by the amination reaction. The acetyl, amine and sulfide groups were estimated through the Fourier Transform Infra-Red Spectra (FT-IR) and the Elemental analysis. The antimicrobial activity of the modified copolymers was tested against various species by the cut plug procedure. It was concluded that the modified copolymers exhibited a satisfied antimicrobial activity towards both Gram positive and Gram negative bacteria. The highly observable result was estimated towards the protous species, at a ratio of 27 % Ethylene and 73% Vinyl Alcohol since the inhibition zone reached 41 mm. The antimicrobial activity increased by increasing the percentage of ethyl groups in the copolymeric material.So, the synthesized polymers were used as biocidal agents for water treatment.