Inspired by the chromogenic reaction of itaconic anhydride and tertiary amine, fluorescent poly(amino ester) polyols are designed and synthesized by melt polycondensation of itaconic anhydride and triethanolamine. The obtained polymers contain no conventional conjugated fluorophores and still display bright fluorescence and good water solubility. The unconventional fluorescence is speculated to be due to the clusters of oxidized tertiary amines and carbonyl groups. Interestingly, the fluorescent polymers exhibit selective sensitivity to specific metal ions, which quench the fluorescence of the polymers. When various metal ions including Na+, Mg2+, A1(3+), K+, Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ba2+ and Pb2+ are added to the aqueous polymer solution, only Fe3+ ions decrease dramatically the fluorescence intensity of the polymer solution. Meanwhile, the quenched fluorescence can be recovered by adding L-cysteine. Therefore, the fluorescent polymers can be applied as new sensing platform for label-free detection of Fe3+ ions and L-cysteine.