A small hydro plant using an Archimedes screw is the focused of this work. This is an alternative solution to smallscale hydropower as it exploits unused resources such as small rivers or streams. Archimedes screw plants reverse the pump use principle and exploit the available stream power for energy production in very low head application. Based on the previous studies, the optimal sizing of Archimedes screws is discussed. Then, a numerical model is established to determine the mechanical efficiency according to its geometrical parameters, its rotational speed and its degree of filling. Simulation results are showed and validated with data from a real installation: this work reports experimental results of a 0.84-m diameter Archimedes screw delivering a torque of 250-N-m. This model is an essential part of the whole electromechanical plant modeling and therefore is useful for the estimation of efficiency, energy production and profitability.