The reaction ratio of sodium pentacyanoammineferroate and aromatic primary amines was examined by the method of continuous variation and the ratio was confirmed to be 1:1. After reacting such primary amines with sodium pentacyano-ammineferroate in 1:1 ratio, the colored solution thereby produced was submitted to the ultraviolet absorption spectra. Such solutions show absorption maxima in the range of 620-735mμ and this absorption maximum can be utilized to distinguish between isomers of aminophenols, phenylenediamines, naphthylamines, and chloroanilines. The colored solution of 1, 4-aminophenol compounds such as p-aminophenol, 2, 4-diaminophenol, 5-aminosalicylic acid, and 1, 4-aminonaphthol shows absorption maximum in the range of 690-710mμ, and color of the solution is very intense and stable. The electron-releasing group (OH, NH2, CH3) indicates hyperchromic effect while electron-attracting group (NO2, HOOC, CH3CO, Cl) shows hypochromic effect. The hydroxyl group in para-position, amino group in ortho-position, and electronattracting group show bathochromic effect.