The nucleus growth rate in the initial stages of thin‐film formation has been discussed on the basis of the collision theory of a two‐dimensional gas and the diffusion theory of surface adatoms. It has been shown that, in the formulation of the area of the capture zone, the former theory is suitable for small nuclei (&rgr; < 0.27) and the latter for large nuclei (&rgr; > 0.27), &rgr; being the ratio of the nucleus radius to one half of the mean diffusion distance of single adatoms. The foregoing theoretical considerations were examined by the deposition experiment of bismuth films onto mica substrates. It has been found that the calculated deposition time, required for obtaining amount of deposits, agrees well with the observed one.