The Co nano-films of different thickness (1—100nm) were successfully deposited on the monocrystalline silicon surface. Atomic force microscope， X-ray photoelectron spectrum (XPS) and X-ray diffraction analyses have been applied to study the surface topography and quality of Co nano-films of different thickness (1—100nm). We found that the deposited grain morphology transformed from acerose cellula by two-dimensional growth to globular aggregates of grains with film thickness increasing when the films thickness was 1—10nm. When film thickness was 3nm, the film had maximal roughness, which then decreased with the film thickness increasing. Atomic concentration and chemical states of cobalt were investigated by XPS scanning. The analysis results show that the chemical states of cobalt in the surface of nano-films are Co, CoO and Co2O3.