The values given in literature for the first and second dissociation constants of oxalic acid at 25°C. vary considerably. For the first dissociation constant some of the vales given are; .038 (Chandler, by conductivity); .17 (Britton, by electrimeric titration; .057 (Drucker); 0.59 (Gane and Ingold, by electromeric titration), and .02 (GLastone), which do not show good agreement. Fir the second dissociation constant, values are; 4.9 x 10-⁵ (Chandler); 6.9 x 10-⁵ (Drucker), 13.8 x 10-⁵ (Britton), 6.4 x 10-⁵ (Gane and Ingold), 3 x 10-⁵ (Glastone) and 5 x 10-⁵ (Pilbrick) which also show poor agreement. In the present work an endeavour is made to determine by an accurate thermodynamic method the true second dissociation constant of oxalic acid at 25°C, 30°C, and 35°C. and the true first dissociation constant at 25°C.