The inhibiting effect of benzotriazole (BTA) on the corrosion of electroplated zinc coatings in acidic sodium sulfate solutions was studied by use of an electrochemical quartz crystal microbalance. Experiments showed that BTA is mainly inhibiting the anodic reaction of the zinc dissolution reaction. In quiescent solution, the rate-determining step of the corrosion process is mass transport of dissolved oxygen to the electrode surface so that BTA does not significantly decrease the corrosion rate. When the solution is deaerated by nitrogen bubbling, the corrosion rate is controlled by the charge-transfer process and the corrosion rate of zinc is greatly reduced by BTA. When the solution is bubbled with air, the corrosion rate increases significantly. The rate of the hydrogen evolution reaction is charge-transfer controlled and the oxygen reduction is controlled by mass transport. (C) 2003 The Electrochemical Society.