A simple, rapid, sensitive and accurate spectrophotometric-method has been developed for the determination of Mercury (II).using the azo-Schiff  reagent 1-(4-(((4,5-dimethyl-1H-imidazol-2-yl)diazenyl)methyl)phenyl)-N-(4-nitrobenzyl)ethan-1-imine(DMIPNI) react with Mercury (II)  solution in the pH= 7 and to form  Red complex. The complex shows λmax at 517 nm with a malar absorptivity 2.44 × 105 L.mo1-1.cm-1 and Sandell’s sensitivity 8.2184×10-4 μg.cm-2 .Beer’s law is obeyed in the concentration range (0.1 – 2 μg.mL-1) of Hg (II) with an extremely high degree of linearity as indicated by the correlation coefficient value of 0.9994 with detection limit of 0.0119 μg.ml-1 and The limit of quantification is 0.0398 μg.ml-1. The nature of complex showed that (M:L) ratio was 1:2 The stability constant of the complex was  2.7368 × 109 mol.L-1 , This spectrophotometric method is considered to be highly sensitive using a detector (DMIPNI).