Recently, the need for smaller axial‐flow fans with high specific speeds leads to the design of counter‐rotating axial fans. The design of this type of machines, which have promising aerodynamic performances, suffers from a lack of knowledge about their aerodynamics. Counter‐rotating rotors, widely studied in aeronautics, are an effective alternative to conventional machines and offer many advantages: rotation ratio and diameter reduction, and high flexibility in use. However, a better understanding of their working and of the rotors interaction is required to enhance their design and to make them widely integrated in current applications. This experimental research work investigates on a ducted counter‐rotating stage designed with a home code, MFT based on an inverse design method for rotors and rotor‐stator stages, and to which a rapid and simple method is implemented to design the rear rotor. The study focuses on the effects of the rotation ratio and on the axial spacing between rotors. It highlights several aspects of the rotors interaction through global performance and local unsteady measurements.