A new spectrofluorimetric method for the determination of trace amounts of iron(II) has been developed. This method is based on the fluorescence quenching of phenanthroline due to the formation of complex Fe(II)-phen. In pH = 4.6-7.1 buffer solution, Fe(II) and phen react to form a red complex. Its composition is established by method of continuous variations and molar-ratio as Fe (II): phen = 1:2. The exitation and emission wavelength are found to be 265 nm and 365 nm, respectively. There is a linear relationship in the range of 24-112 ng.mL-1 for Fe(II). The detection limit of Fe(II) is 4.1 ng.mL-1. This method is simple and rapid, and has been applied to the determination of iron in the chinese herbal medicine.