Reaction of o-phenylenediamine and 8-formyl-7-hydroxycoumarin yield a new coumarin salen ligand, (CSB) which was isolated as orange air-stable solid and characterized by melting point, thermogravimetric analysis (TGA), mass spectra, infrared and NMR (1H, 13C) spectroscopy. New CSB was dispersed in nafion and nafion-CSB composite was deposited on a glassy carbon electrode. The modified electrode nafion-CSB/GCE allowed the formation in-situ of mercury film for detection of Pb (II) and Cd(II) by anodic stripping voltammetry (ASV) in buffer phosphate solution pH 3.0 and 4.0. Optimal conditions were studied (mercury concentration: CHg 40.0 mg L-1; CSB concentración; CCSB; 20.0 μmol L-1; pH 3.0 and pH 4.0; EACC:-1.1 V and tACC: 80).The detection limit (3s/b) for Pb (II) Cd (II) were of 0.15 μg L-1 for Pb(II) and Cd(II) at pH 3.0. Moreover, 0.071 and 0.080 μg L-1 for Pb(II) and Cd(II), respectively at pH 4.0, The method was validated using ICP multi-element standard solution IX (Merck) containing As, Be, Cd, Cr(VI), Hg, Ni, Pb, Se and Tl 100 mg L-1. Finally, river, tap and mineral waters were analyzed.