Constant current charging curves from 10−6 to 10−1 A‐cm−2 are used to study the mechanism of growth of anodic oxide films at platinum in solutions. At any constant current density the potential initially changes linearly with time. In this linear region no is evolved. The linear region is followed by a region in which potential changes logarithmically with time while oxygen evolution becomes the predominant reaction. The thickness of the oxide films at which the transition occurs depends on the applied current density but for all current densities it is less than 10Å. Both in the linear and the logarithmic region the ellipsometric thickness‐time relationships essentially parallel the relationships. The rate of growth is described by where is the thickness and the potential at which oxide film starts to grow. From the transfer coefficient α, that is equal to 158 Å‐V−1, it was deduced that the oxide phase is composed of divalent platinum ions, i.e., the oxide phase is . It is suggested that the rate‐determining step is a process at the metal/oxide interface rather than a process at the oxide/solution interface or a process within the bulk of oxide. The distribution of the potential between the oxide film and the double layer is discussed. It is shown that the potential difference across the solution double layer is constant for the growth at current densities examined here. This is possible if the electrochemical reaction in the double layer is fast.