The complex bis-(L-histidinato)nickel(II) monohydrate has been synthesized and structurally characterized by single-crystal X-ray diffraction. This complex was solved in the monoclinic system, space group C2, with the following unit-cell parameters: a = 29.313(6) angstrom, b = 8.227 (2)angstrom, c = 6.264(1) angstrom, alpha = 90 degrees, beta = 90.189(5)degrees, gamma = 90 degrees, Z = 4, V = 1510.5(5)degrees A(3). The final R value was R1 = 0.0301 for 7558 measured reflections.