The thickness dependence of the surface roughness and the grain size of nanosilicon films, produced by low-pressure chemical vapour deposition, has been found, by using atomic force microscopy. A correlation between the surface roughness, grain size, and transformation of a film structure from the equiaxial structure into a fibrous one is established. Possible mechanisms of surface evolution are analyzed. K e y w o r d s: nanosilicon films, surface roughness, grain growth, mechanism of grain growth, atomic force microscopy.