The mechanism of direct copper plating on nonconductive resin substrates was studied using high-resolution TEM, SEM and XPS. Substrates were catalyzed by Pd/Sn catalyst and subsequently immersed in alkaline solution containing either copper ions or sulfide ions before electroplating. After conversion in the alkaline solution containing copper ions, catalyst colloid particles formed clusters and crystallinity improved. Sulfide compounds, however, formed by conversion in alkaline solution containing sulfide ions. Both conversion techniques markedly promoted propagation in electroplating. The effect is explained by propagation in which improved palladium colloid crystallinity and palladium sulfide formed in conversion play a critical role in determining the propagation rate.