In present study, four antiinflammatory agents, namely naproxen, indomethacin, ibuprofen and etodolac were titrated potentiometrically using tetrabuthylammonium hydroxide in acetonitrile and 2-propanol solvents under nitrogen atmosphere at 25 degrees C. The ionization contants of several non-steroidal antiinflammatories have been determined potentiometrically in a series of acetonitrile. Four antiinflammatory agents are non-steroidal antiinflammatory drugs of the family of carboxylic weak acids. The results are compared with octanol-water media. Acetonitrile has a relatively high dielectric constant (epsilon = 36) and a small autoprotolysis constant (pK(s) = 33.6). Acetonitrile is higher dielectric constant than octanol. Because of this reason, ionization constant in acetonitrile is lower than in octanol-water mixtures.