AbstractThe mechanism of electroless copper deposition with formaldehyde from alkaline ethylenediamine‐tetraacetate (EDTA)‐containing solutions was studied. Oxidation and reduction could be investigated separately by use of a quartz microbalance in combination with fast solution exchange. It could be confirmed that the reaction is predominantly electrochemical, no indication for a direct electron transfer from a reducing agent to copper ions could be detected. In spite of this the oxidation and the reduction reaction are not independent. Formaldehyde oxidation on copper surfaces is enhanced when simultaneously copper ion reduction takes place. Formaldehyde, on the other hand, does not only act as an electron donor but also generates a catalyst for the copper ion reduction. We suggest that chemisorbed methanediolate anions catalyze the reduction. It can be shown that other substances, which either have a similar structure element as methanediolate or which are known to be specifically adsorbed on copper, also catalyze the copper ion reduction from alkaline, EDTA‐containing solutions.