A new method for the determination of nickel(II) with dibromo-p-methyl-arsenazo by spectrophotometry has been proposed. The apparent molar absorption coefficient of method is ε612 nm = 1.01 × 104 L·mol-1·cm-1. Beer’s law is obeyed over the range of 0.10 ~ 3.5 μ g / mL for nickel content. The detection limit of method is 0.11 μ g / mL. The present method has been satisfactorily applied to the determination of nickel in rain water.