Abstract: It is reported that iron(Ⅲ) forms a red complex with potassium thiocyanate and 1,10-phenanthroilne in the presence of Tween-20 and in nitric acid solution. The absorption maximum wavelength of the complex is 518nm. and it's apparent mole absorptivity is 2. 06 104 L mol-1 cm-1. Beer's law is obeyed for iron in the range of 0-50 g/25mL,correlation coefficient is 0. 9999. The advantages of this method are simple operation. less time-consuming. high selectivity and repeatability. It has been applied to determine iron in plant with satisfactory results, without the need for preliminary separation and masking steps.