The preparation, spectroscopic, magnetic properties and crystal structure of [Cu(en)2(OH2)2][stz]2·2H2O (en = ethylenediamine; stz stands for the deprotonated form of sulfathiazole, 4-amino-N-2-thiazolylbenzenosulfonamide) are reported. The complex crystallizes in the triclinic system, space group P1, with cell constants a = 8.321(1) Å, b = 7.441(1) Å, c = 13.627(3) Å, α = 86.02(1)°, β = 101.81(1)°, γ = 97.88(1)° and Z = 1. The metal ion is six coordinate by four N atoms of two ethylenediamine ligands in the basal plane and two O atoms of two water molecules in the axial positions. The stereochemistry of the metal center is irregular and can be considered a distorted octahedron. Two deprotonated sulfathiazole molecules are present in the complex and a center of symmetry is located at the copper(II) ion. This is the first crystallographic evidence of sulfathiazole acting as a counter ion. The susceptibility of certain strains of bacterium towards the complex was measured, it shows good antibacterial activity against Salmonella typhimurium strain. Keywords: CopperAntibacterialEthylenediamineSulfathiazole