Thin metallic Mn films of various thicknesses were thermally vapour-deposited on glass substrates at room temperature in a high vacuum. The electrical conductivity of these Mn films was measured in situ as a function of film thickness and annealing temperature. The experimental results indicate that the electrical resistivity decreases as the film thickness and annealing temperature increase. The calculated values of the activation energy for electric conduction decrease as the film thickness increases. The mean free path and mobility for charge carriers, and the electrical resistivity of infinitely thick films, were calculated as a function of temperature; they are in good agreement with the theoretical relationships.