A simple flow injection method is proposed for the determination of nickel by its complexation with ammonium 2-amino-cyclohexene dithiocarbamate (AACD). The dark red complex can be detected by spectrophotometric determination at 535 nm. The FIA factors that influence on sensitivity were optimized by factorial design analysis. The model of absorbance vs. these factors was constructed and the correlation of these factors with each other was studied. Nickel can be determined as low as 0.007 μg/ml and Beer's law was obeyed in the range of 0–2.5 μg/ml of Ni(II). The effect of more than thirty potential interfering cations and anions were studied. The evaluation of the method was examined by the determination of Ni(II) in hydrogenated vegetable oil and synthetic samples.