Time-dependent extended X-ray absorption fine structure (QEXAFS) measurements using the total external reflection geometry were used for the in situ investigation of the potentiostatic silver oxide formation in 1 M NaOH. It is demonstrated that this EXAFS tool yielding near range order structural information is well suited for time-resolved studies of electrode surfaces under potential control. As examples, the initial growth stages of thin silver(I) oxide layers are presented as well as changes of the near range order of thick Ag2O films induced by potentiostatic transients. A comparison of the experimental results with those of model calculations permits the determination of the reaction kinetics of electrochemical phase formation.