Gold and glassy carbon electrode surfaces were modified with L-cysteine, and the electrochemical behavior of ascorbic acid (AA) was investigated on these new surfaces. To improve the efficiency of electrodes, the electrode surfaces were modified and optimum conditions for AA determination were established. Electrochemical experiments were performed at different potential ranges, the concentration of AA, scan rates, number of polymerization cycles and pH values. Using cyclic voltammetry (CV) technique, optimum conditions were determined as the potential scanning range of 0.2 to 1.5 V vs. Ag/AgCl in 0.1 M phosphate buffer solution (pH 7.02) for the L-cysteine/Au electrode, and-1.95 to 1.9 V vs. Ag/AgCl in 0.1 M phosphate buffer solution (pH 2.7) for the L-cysteine/GC electrode. For the characterization of both modified electrode surfaces, a series of physicochemical techniques was also applied. The usability and selectivity of these two proposed modified electrodes for the determination of AA were investigated using square wave voltammetry (SWV) in the presence of possible interferents, i.e., glycine, L-glutamic acid and uric acid.