Abstract: The color reaction of nickel with p-nitrophenylfluorone (p-NPF) in microemulsion has been studied. Nickel (Ⅱ) reacts with p-NPF to form a stable 1:3 complex at pH 10.4. Its apparent molar absorptivity is 1.64×10⁵L/(mol·cm) at 600 nm. Beer's law is obeyed in the range of 0～0.7 μg/mL. The coexistent metal ions can be separated and nickel can be enriched by sulphydryl dextrane gel (SDG), greatly improving the selectivity and sensibility of system. The method is used to determine trace amount of nickel in human hair samples with satisfactory results.