Molecular orbital study was applied to investigate electroless deposition processes, focusing upon reducibility of reductants as well as the effect of catalytic activity of the metal surfaces. Elementary reaction pathways of the reductants such as dimethylamine borane, hypophosphite ion, formaldehyde, and titanium trichloride were quantitatively examined in terms of the heat of reaction. It was indicated that the reaction via 5-coordinate intermediates was favorable for these species and that the value could be used for quantitative evaluation of the reducibility of the reductant species. The analysis of solvation effect on the reactions suggested that the reactions preferably proceed at the interfacial region, i.e. the surface of the metal, rather than in the 'bulk' solution region. The effect of catalytic activity of metal surfaces was investigated using a cluster-model surface. It was suggested that the elementary reactions were stabilized on the metal surfaces to enhance the electron emission from the reductants. On the other hand, difference in the stabilization effects for the reaction of hypophosphite ion was obtained due to the variation in the metal species, it was expected that the copper surface is not catalytically active for the reaction, which corresponds to the experimentally known results.