Nickel complexes of Thioglycolic acid have been investigated by potentiometric technique in 40% V/V ethanol. It was found that nickel forms colourless 1:2 complexes. The stability constant of the complexes formed have been determined by applying Calvin and Melchior’s extension of Bjerrum’s method at three different temperature. The values of log K1, log K2 at 298 K, 7.52, 4.65 at 303 K, and 8.13, 5.66and at 308 K 8.26 and 5.78 respectively in 40% ethanol medium. There is no reference in the literature regarding the complexing tendency of thioglycolic acid with nickel ion in 40% aqueous-ethanol medium. Hence the present investigation has been initiated. The composition and stability constant of the complexes have been studied by potentiometric method. The value of thermodynamic parameters DG, DH, and DS have also been calculated.  he values of overall changes in DG, DH and DS, at three different temperature accompanying the reaction have also been evaluated in 40% ethanol medium the values are –47.1668 KJ mol-1, –32.8369 KJ mol–1, –0.261392 KJ mol–1, +154.801 J/K and +107.50 J/K respectively.