The stability constants of the complexes which were formed N-salicylidene-L-cysteine with iron (II), iron (III), cobalt (II), nickel (II), coppper (II) and zinc (II) were determined potentiometrically by using CALVIN-BJERRUM and IRWING- ROSSOTTI methods, in this work. The protonation constants or dissociation constants of the ligand were found as logK1 or pK₃ =11,99 as log K₂ or pK₂=10.15 ; as logK₃ or pK1= 8,75 at 25° and for I=0,11. Also the overall formation constants of complexes were found as logβ₂= 33.95 for iron(II); as logβ₂ = 36,00 for iron (III); as logβ₂ =28,00 for cobalt (II); as logβ₂ =19,90 for nickel(II); as logβ₂= 8,40 for copper(II); as logβ₂= 21,30 for zinc(II) at 25°C and for I = 0,11. The conditional formation constants and the formation pH ranges of complexes were determined. The composition of metal complexes were determined as metal/ligand =½, except for copper complex. The composition of copper complex was determined as metal/ligand = 1/1. Keywords :