<p>Casing treatment is a commonly used flow control technique in axial compressors, which effectively improves aerodynamic stability but often results in an efficiency penalty. This study improves the stall margin while reducing these penalties by combining a self-recirculating casing treatment with axisymmetric shroud end wall contouring on a transonic axial compressor stage. Numerical results show that the stall margin of the baseline compressor stage is improved by 5% with little efficiency penalty at lower flow region. Adding the axisymmetric shroud end wall contouring further improves the stall margin by 1% and increases the efficiency by up to 0.7%. These positive effects are found associated with the geometry of the axisymmetric shroud contouring. With a concave shape of the rotor (convex shape of the casing) in the front part of the rotor passage, the pressure difference across the rotor tip clearance is reduced near the leading edge and is increased in the mid-chord region. This significantly reduces the loss core of the tip leakage vortex, improving efficiency and stall margin. The corner separation in the stator is also relieved due to a better outflow of its upstream rotor. The numerical study shows that the above positive effects increase with maximum contour height.</p>