A reaction between nickel(II) sulfate and hydrazine in aqueous solution yields blue crystals of [Ni-6(N2H4)(6)(SO4)(4)(OH)(2)(H2O)(8)] (SO4)(H2O)(10). The compound has been characterized by single, crystal and powder X-ray diffraction, vibrational spectroscopy, as well as variable-temperature magnetic susceptibility. This is the first reported crystal structure of the nickel(II) complex with hydrazine. The complex cation in the compound has a remarkable structure with unusual diversity of bridging groups including hydrazine molecules, sulfate ions, and hydroxo groups. Hydrazine molecules bridge nickel ions into trimers, which are further linked into hexamers through bridging sulfates. The magnetic susceptibility study of the compound reveals antiferromagnetic interaction between nickel(II) ions in the polynuclear complex.