The initial growth process of silver nanoparticles on highly oriented pyrolytic graphite (HOPG) and amorphous carbon (a-C) was studied. Scanning tunneling microscopy was used for analysis of the nanoparticles formed on HOPG. Transmission electron microscopy was employed to study the growth procedure on a-C. The number densities (D-n) of silver nanoparticles on both HOPG and a-C remain constant at a very early stage, then both decrease with deposition time and have a saturated value. The D-n, decrease suggests migration followed by impingement. We found evidence of migration of 5 nm particles on a-C. Interpretations are given to explain the impingement and shape change of the silver nanoparticles.