Stability constant of Iron(III) gallic acid complxes had been measured potentiometrically. The experimental results of these potentiometric titrations were treated by well known computer program ''Best''. The values were further refined till least sigma fit i.e. 0.02. For thermodynamic study the change in log beta values at different temperatures were also examined and entropy and enthalpy of these reactions were determined. Iron(III) complexes of gallic acid methyl ester were prepared in the same way, and the above results were compared with this new complex. The role of carboxylate group on the complex were noted. The beta values of these two complexes were then compared with other iron complexes and their biological importance were also discussed.