The extraction equilibrium of picolinic acid using trialkylamine (N235) dissolved in n-octanol at 298 +/- 0.5 K has been studied. The factors that affected distribution coefficients (D), such as aqueous equilibrium pH (pH(eq)), N235 concentration, and diluents, were investigated. As diluents, n-octanol showed higher D values than those of tetrachloromethane and kerosene. The maximum D values appeared at a N235 concentration of 0.4218 mol.L-1, which were in agreement with the results of the apparent alkalinity of N235/n-octanol. The D values were also observed with peak values at pHeq in the range of 4.5-6.0. In addition, D decreased with the increase of the initial picolinic acid concentration. Fourier transform infrared spectrometry confirmed that pH(eq) had no influence on the complexes' structure and the extraction reaction belonged to the proton-transfer process. The expression of D was proposed based on the mass action law with reasonable assumptions, and the model parameters were calculated by fitting the experimental data. The D values obtained by the model were in good agreement with the experimental ones.