Abstract“In‐Situ” observation of nucleation and growth of Ag crystallites on graphite substrate by vapour deposition was carried out by scanning electron microscope (SEM). Irradiation of the SEM electron beam onto the substrate surface before and during deposition enhanced Ag nucleation. The density of the Ag crystallites was 1010/cm2in room temperature condensation, but decreased to 109/cm2in high temperature condensation at 140 °C. When the substrate was heated after room temperature condensation, the density of the Ag crystallites decreased prominently. This means that coalescence of the Ag crystallites takes place as a result of their migration on the sub