A bis(hexaaquanickel(II)) complex-decavanadate cluster compound, (NH₄)₂[Ni(H₂O)₆]₂V₁₀O₂₈ ⋅ 4H₂O, was synthesized. This compound has been structurally characterized by infrared spectroscopy and single crystal XRD analysis that indicated its triclinic P −1 space group. Additionally, the thermal decomposition mechanism of the compound to a composite of V₂O₅ and Ni(VO₃)₂ was elucidated. The common antibacterial agents are organics that experience instability and cause pollution to the environment, therefore we wish to consider the synthesis of inorganic bactericides. (NH₄)₂[Ni(H₂O)₆]₂V₁₀O₂₈ ⋅ 4H₂O, in comparison to chloramphenicol, led to better inhibition of the growth of five Gram negative human pathogenic bacterial strains (Escherichia coli, Klebsiella pneumonia, Serratia marcescens, Serratia plymuthica and Pseudomonas aeruginosa). Remarkably, the highest inhibition was displayed against Escherichia coli that was inhibited completely at (NH₄)₂[Ni(H₂O)₆]₂V₁₀O₂₈ ⋅ 4H₂O (50 μg/ml), while the Escherichia coli growth was of 12.93×10⁷±0.25 CFU/ml at (NH₄)₂[Ni(H₂O)₆]₂V₁₀O₂₈ ⋅ 4H₂O (5 μg/ml). This is in contrast to chloramphenicol (5 μg/ml) that allowed for Escherichia coli growth of 13.97×10⁷±0.24 CFU/ml (control=17.33×10⁷±0.48 CFU/ml).