Cobalt complexes of Thioglycolic acid have been investigated by potentiometric technique in 40% V/V acetone. It was found that cobalt 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, 30ºC and 35º C have been found to be 7.85, 6.36, at 298 K, 8.01, 6.50 at 303 K, and 8.10, 6.78 at 308 K, in 40% acetone medium respectively.