The oxidation (electron emission) mechanism of a hypophosphite ion (H2PO2, which is a representative reducing agent for an electroless deposition process, was studied by an ab initio molecular orbital method. Two types of reaction pathways were examined, namely, the pathway via three-coordinate compound obtained by primary dehydrogenation, and the one via five-coordinate compound by primary addition of OH-. The calculated energy profile showed that the oxidation reaction occurs via five-coordinate compounds. The solvation effect is clarified to make the reaction endothermic, indicating that the reaction preferably proceeds at the solid/ liquid interface, i.e., the surface of the deposits. rather than in the solution bulk. The catalytic activity of the metal surfacer which is one of the most significant factors for the electroless deposition process, was also investigated using Pd-n (n = 4-7) clusters as a model surface. It was found that one of the most important characters determine the catalytic activity of the deposited metal is the electron-accepting ability from the reductant.