The Wells turbine is a well-known axial turbine used to extract energy from a bidirectional airflow generated by ocean waves in an oscillating water column (OWC) power plant. Focus of this study is the design and experimental investigation of optional guide vanes. Starting point is a known analytical design method for guide vanes, modified to take into account the bidirectional flow. A series of guide vanes was designed and manufactured. Eventually the turbine’s aerodynamic and acoustic performance including these guide vanes was investigated on an aero-acoustic test rig. Guide vanes increased peak efficiencies by some 10 % points as compared to the reference turbine without guide vanes, however, at the expense of the stall margin. Furthermore, tonal noise was found to become more pronounced with guide vanes. However, selecting a larger rotor-stator gap and applying a positive stator vane lean proved to mitigate the noise relevant rotor-stator interaction without penalty on efficiency.