A novel fluorescent chemosensor in which two aza-18-crown-6 moieties are linked to a coumarin fluorophore has been synthesized for sensing Fe3+. The selective fluorescence enhancement was observed upon binding Fe3+ at physiological conditions (pH=7.4, [NaCl]=0.135M, [KCl]=0.01M), whereas other metal ions, such as Li+, Na+, K+, Mg2+, Ca2+, Cu2+, Zn2+, Co2+, Ni2+, Mn2+, Hg2+ and Pb2+ produced no effect.