Magnese complexes of Thioglycolic acid have been investigated by potentiometric technique in 40% V/V ethanol. It was found that magnese forms colourless 1:2 complex. 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 25º C, 30º C and 35º C have been found to be 6.87, 4.16, at 298 K, 7.11, 4.22 at 303 K, and 7.31, 4.38 at 308 K, in 40% ethanol medium respectively. The values of overall changes in DG, DH and DS, at three different temperature accompanying the reaction have also been evaluated at 303 K and the value of DG1, DG2, DH, DS1, DS2, are found to be -42.120 KJ mol-1 -33.610 KJ mol-1and -0.1019KJ mol-1 +151.0267 J/K, +122.1058 J/K in 40% ethanol medium.