An enantioselective potentiometric sensor was constructed by immobilizing chiral salen Co(II) complex on an indium tin oxide (ITO) electrode modified with self-assembled monolayer of (3-aminopropyl)triethoxysilane (APTES). The proposed sensor displayed an excellent Nernstian slope of -58.6 +/- 0.6 mV decade(-1) in a linear range of 1 x 10(-5) to 1 x 10(-2) mol L-1 toward D-mandelic acid (D-MA) and its enantioselcctivity coefficient for the counter isomer (L-MA) was -2.71, indicating that the sensor possesses excellent chiral discrimination ability.