Acid dissociation constants and chelate stability constants of 8-hydroxyquinoline-5-sulfonic acid have been determined for divalent metal ions. Co (Ⅱ), Ni (Ⅱ) and Zn (Ⅱ) by means of the Calvin-Bjerrum technique at the various temperatures. The standard free energy changes for the reactions at $20^{circ}$, $30^{circ}$, $40^{circ}$and $50^{circ}C$ were calculated, and the corresponding values of ${Delta}H^{circ}$ and ${Delta}S^{circ}$ applying over this temperature range are reported. The results are interpreted on the basis of current theories of metal chelate formation in aqueous solution.