A differential pulse voltammetry (DPV) method for the determination of lactic acid (LA) was developed with a glassy carbon electrode. LA causes the appearance of new paired peaks at a more positive potential during the reduction of 1,4-benzoquinone (BQ).The new peaks are attributed to the drastic change in pH at the electrode surface. As proton donors, LA provides protons and inhibits the pH increase at the electrode surface. The height of the new cathodic peak is dependent on the concentration of LA but is independent of BQ, phosphate, and insoluble solid matter in yogurt. The cathodic peak potential is dependent on the acid pKa, which can be used to identify the other adulterated acids in yogurt. The proposed method was performed to measure the LA content of untreated yogurt samples. Results were consistent with those obtained by the potentiometric titration method.