A highly viscous 3D flow from the centrifugal impeller greatly affects the diffuser aerodynamic performance. The flow at impeller exit is invariably distorted along the blade span, which cause the mismatch of flow angle at the diffuser end-walls and eventually leads to corner and boundary layer separation. To reduce corner flow separation and to extend the blade loading limit of diffuser, blended blade and end-wall (BBEW) technique is used. The present numerical study is conducted to investigate the overall stage performance of the highly loaded centrifugal compressor, when equipped with diffuser by considering two configurations: one with planar blade and end-wall (base case) and another with blended blade and end-wall. Geometrical changes are brought by changing the fillet radii (Rf) around the blade and end-wall junction. Reynolds-Averaged Navier–Stokes (RANS) method was used to resolve the flow field inside the rotor and diffuser passage. Numerical results show that diffuser with blended blade and end-wall improved the stage efficiency by 0.77% relative to the base case. Flow phenomena are presented by velocity stream lines and to account for energy losses, turbulence kinetic energy (TKE) is shown as contour plots.