A model has been assumed to predict the hydraulic and disc friction losses in a radial compressor stage. A potential three dimensional flow field inside the impeller is solved, by using TSONICMR program. Then, the hydraulic and disc friction losses sere predicted for the impeller, vaneless diffuser and the collector. Experimental investigation has been carried out for a radial compressor stage, in order to verify the validity of the assumed model. The pressure ratio and efficiency were measured for different mass flow rats. at different rotating speeds. The results showed satisfactory agreement with that predicted .