Conventional Savonius rotors have low performance such as low coefficient of power and low coefficient of torque. In order to increase this performance, a helical Savonius rotor with a twist of 180 is proposed. In this paper, we are interested in studying the aerodynamic behavior of the helical Savonius rotors installed in an open jet wind tunnel. Particularly we are interested in studying the influence of variation of Reynolds number and the overlap ratio on the performance of a modified Savonius rotor with aspect ratio of 1.57 at a Reynolds numbers equal to Re = 79,794, Re = 99,578, Re = 116,064 and Re = 147,059. Results conclude that the variation of Reynolds number and overlap ratio has an effect on the global characteristics of the helical Savonius rotor. A comparison between the helical one and the conventional one shows that the maximum power coefficient of the Savonius wind rotor is higher. This work is developed at Laboratory of Electro-Mechanical System (LASEM) of the National School of Engineers of Sfax (ENIS). (C) 2012 Elsevier Ltd. All rights reserved.