Five new 4- or 8-substituted-7-hydroxycoumarin derivatives (1-5) were synthesized as fluorescent sensors for metal ions. Fluorescent changes and selectivity for metal ions were compared based on the introduction of different ligands and/or testing with different substitution positions of 7-hydroxycoumarin in aqueous solution. Especially, probes 2, 3 and 5 displayed large fluorescence enhancements with Zn 2+ and Cd 2+. Probes 2 and 3 showed moderate selectivity for Zn 2+ over Cd 2+. On the other hand, probe 4 showed large fluorescence quenching effects upon the addition of Ag + and Hg 2+.