The active electrode area, capacitances, and resistances of MWNT-film coated glassy carbon electrodes with different amount of MWNTs have been characterized by cyclic voltammetry and chronoamperometry. They are varied by controlling the amount of MWNTs dispersed on the electrode surface and affect the voltammetric responses of analytes in liquids. The redox current of acetaminophen is enhanced on the MWNT-film coated electrodes due to the enlarged active electrode area. The oxidation of acetaminophen occurs at 0.34 V and the reduction occurs at 0.27. Two electrons and two protons participate in the reversible redox reaction. The diffusion-controlled anodic peak current is proportional to the concentration of acetaminophen from 5.0 to 0.1 mM with a detection limit of 2.4 mu M. The determination of acetaminophen in pharmaceutical formulations was also conducted.