The effects of substituents on the reactivity of the monosubstituted anilines with fluorescamine (FLA) and the fluorescent properties of the reaction products, FI (Ph), were investigated. Generally, the substituent at o-position markedly inhibited the reactivity of the amino group (ortho-effect). While the electron-donating substituent seemed to be favorable for the formation of FI (Ph), the electron-attracting one seemed to lower reactivity of the amino group. However, the presence of the latter substituent led to the enhanced fluorescence of FI (Ph). The highly significant correlation was observed between the wavelengths (nm) of the emission maxima and the Hammett's substituent constants.