The mechanism of direct copper plating on nonconducting resin substrates was investigated by high resolution transmission electron microscopy and scanning electron microscopy observation and surface analysis techniques. The substrates were catalyzed by Pd/Sn mixed catalyst and accelerated in an alkaline solution containing copper ions and a reductant before the direct plating. After the acceleration, copper crystalline particles measuring approximately 300 nm were found to be dispersed at the population density of 1.4 X 10(11) m(-2) in addition to adsorbed palladium colloids. The colloids formed clusters measuring 20 to 50 nm which consist of individual particles measuring approximately 2 nm. The addition of copper ions in the acceleration solution exerted a remarkable promotion effect on the speed of lateral propagation of direct plating. This effect can be explained by a modified stepwise propagation mechanism in which dispersed copper particles formed in the Cu(II) containing accelerating solution play a critical role in determining the propagation speed. The copper particles also play an important role in determining the uniformity of the propagation of copper plating.