The paper represents the equilibrium study on reactive extraction of pyridine-3-carboxylic acid (NA) and pyridine-4-carboxylic (iNA) acid from aqueous solution by N, N-dioctyloctan-1-amine (TOA) dissolved in five different diluents [dodecane, methyl benzene, decan-1-ol, 4-methylpentan-2-one (MIBK), and chloroform] at constant temperature of 298 +/- 1K. According to an experimental study, the extraction ability of diluents with TOA is found to be in the order of chloroform>decan-1-ol>MIBK>methyl benzene>dodecane for both acids. The highest extraction efficiency in terms of the distribution coefficient (K D) is found to be 45.15 and 25.79 for NA (0.12mol center dot dm3) and iNA (0.03mol center dot dm3), respectively. The values of loading ratio, Z (between 0.194 and 0.512) for both acids indicate the formation of 1:1 acid-TOA complexes in the organic phase. The values of the equilibrium constants (K 11) are determined from the experimental data using mass action law. These estimated values of K 11 are compared with the predicted values of K 11 from relative basicity and linear solvation energy relationship (LSER) models. The LSER model predicts the K 11 with an error limit of +/- 3% for NA and +/- 2% for iNA.