The asymmetric unit of the title compound, [Ni(C(10)H(9)N(4)O(2)S)(2)(C(5)H(5)N)(2)]·0.5H(2)O, contains the distorted octa-hedral trans-[Ni(sdz)(2)(py)(2)] (sdz is the sulfadiazine anion and py is pyridine) complex mol-ecule and half of a water mol-ecule. A three-dimensional network is generated by N-H⋯O and O-H⋯O hydrogen bonds and C-H⋯O inter-actions between the complex and the water mol-ecules.