We investigated the effect of ferric ion absorbance on the detection of Fe 3+ by fluorescent sensors. The presence of Fe 3+ ion resulted in a decrease of emission intensity of fluorophores (naphthalene, dansyl chloride, and anthracene) excited with UV light. Absorbance spectrum and reversibility studies revealed that the decrease in emission intensity of the fluorophores without a receptor moiety was mainly due to the absorbance of ferric ion. We synthesized fluorescent chemical sensors consisting of the receptor for Fe 3+ and naphthyl fluorophore or dansyl fluorophore, respectively. The sensors detected Fe 3+ by a fluorescent quenching effect of Fe 3+ , as well as by the absorbance effect of Fe 3+ . The absorbance of Fe 3+ has a considerable interference effect on the excitation of the fluorophore with a short excitation wavelength range in UV light. Hence, fluorophores with longer excitation wavelength are highly recommended in the synthesis of fluorescent sensors for Fe 3+ .