The nucleation rate of gold on the cleavage face of muscovite mica in UHV was studied as a function of substrate temperature for 403°–515°K and of impinging flux for 0.6–1.8×1013cm−2sec−1. This range of substrate temperature and flux values was selected to yield growth conditions consistent with analysis of the nucleation rate data in terms of the atomistic nucleation theory of Walton. Gold was evaporated from a wire maintained at a temperature below the gold melting point and positioned near the mica substrate so that various regions on the mica were exposed to different fluxes with accurately known relative values. The mica was subsequently thinned and examined by transmission electron microscopy to determine the initial nucleation rate. The low‐temperature nucleation rate data gree reasonably well with the atomistic nucleation theory of Walton, while the high‐temperature data show two peaks in nucleation rate.