The reactive extraction of benzoic acid (BA) and pyridine-3-carboxylic acid (NA) using diluent mixtures, decane-1-ol (w = 0.36) + cyclohexane (w = 0.64) and 4-methylpentan-2-one (w = 0.63) + kerosene (w = 0.37) with and without reactive extractants such as tri-n-butylphosphate (TBP) and N,N-dioctyloctan-1-amine (TOA), is carried out. The effect of various parameters such as the type of acid, type of diluent mixture, type of extractant, and composition of aqueous and organic phases are studied to analyze the performance of reactive extraction. The maximum values of the distribution coefficient (K(D)) are found to be 38.1 for BA and 7.4 for NA with TOA (0.229 mol . dm(-3)) in decane-1-ol (w = 0.36) + cyclohexane (w = 0.64). A mathematical model based on mass action law is proposed to estimate the values of partition coefficient (P) and dimerization constant (D) in physical extraction and equilibrium constants (K(E)) and number of reacting extractant molecules per acid molecule in chemical extraction. The values of the loading ratio, Z (between 0.005 and 0.566), for the extraction of both acids using TBP and TOA in both diluent mixtures indicate a formation of a 1:1 acid/extractant complex in the organic phase. For the reactive extraction of both acids, the highest values of K(E) are found with TOA in decane-1-ol (w = 0.36) + cyclohexane (w = 0.64).