In this study, a novel mercapto-terminated trinuclear Ni(II) complex (Ni3) was synthesized and used as electrocatalysts for the detection of hydrazine hydrate in real water samples. The as-prepared Ni3 molecules possess six thiomethyl groups at the periphery of the complex;such SCH 3 groups can react with Au electrodesto immobilize the Ni3 molecules on their surface through the formation of a self-assembled monolayer. The Ni3-modified Au electrode (Ni3/Au) demonstratedits excellent electrocatalytic activity for the oxidation of hydrazine hydrate through the significant decrease in the overpotential.Chronoamperometry study showed a diffusion coefficient (D) of 5.82×10 −5 cm 2 ·s −1 and acatalytic rate constant of 8.57×10 3 M −1 ·s −1 . Using square wave voltammetry (SWV) technique, this Ni3/Au electrodebased hydrazine hydratesensor exhibiteda high sensitivity in quantitive analysis, and the detection limit could be as low as ~0.07 μM with a linearity ranging from 0.2 to 50 μM. Additionally, the good reproducibility, anti-interference performance, and long-term stability made the proposedsensor be capable of detecting trace level of hydrazine hydrate in real water samples.