Distribution of iso-nicotinic acid (NA) between water and trialkylamine (Alamine 336), dissolved in different diluents (1-octanol, tetrachloro methane, and kerosene), has been studied. The influence of the pH value of aqueous solutions, the Alamine 336 concentration, and diluents on distribution ratio (D) has been discussed. The extraction mechanism of Alamine 336 on NA has been deduced according to the results of Fourier transformation infrared spectrometry. Results indicate that the diluents, the Alamine 336 concentration, the pH value of aqueous solutions, and the initial NA concentration are the key factors that affect D. The polar diluent (1-octanol) is favorable for extracting NA when Alamine 336 is used as extractant. D increases with the increasing Alamine 336 concentration and creates a higher D range vs the equilibrium aqueous pH range of 4.8 to 5.5. The proton-transfer reaction is demonstrated in the extraction process. An expression of equilibrium D was proposed, and the parameters of the apparent extraction equilibrium constants (K) and the complex ratio (n) (iNA vs Alamine 336) were calculated by fitting the experimental data. It was found that the K and n are 47.8 (mol(.)dm(-3))(-1/2) and 2: 1 with 1-octanol as diluent and 4.72 (mol(.)dm(-3))(-2) and 1:2 with kerosene as diluent, respectively.