The kinetics of formation and the structure of copper layers are investigated in the presence of a complex additive for bright acid copper plating. It is shown that, in the presence of additive, two maxima are observed on the voltammetric curve. The first may be explained in terms of the formation of a complex between the components of the additive and the cuprous ion. The structure of the initial copper deposits is studied using the double pulse technique. It is shown that the size of separate crystallites strongly decreases in the presence of the additive which also blocks vertical growth and favours lateral growth.