Abstract: The GCr15 steel city rail bearing outer rings were heat treated by four different processes，and the effect of heat treatment processes on microstructure and hardness of the outer rings was studied by SEM and TEM observation，hardness testing and residual stress measurement. The results show that the average hardness of the quenched，quenched and tempered， austempering (for 1 h and 3 hat 210 ℃) outer rings was 861，750，835， 701 HV. The microstructure of austempering outer rings was mannly composed of martensite and lower babrite. The lower bannite content of the outer rings aus tempered for 1 h was about 30% less than that of the outer rings aus tempered for 3 h. The best heat treatment process for GCr15 steel bearing outer rings was austempermg for 3 h at 210 ℃ after 20 min intsulation isothermal at 860 ℃. After above heat treatment， the surface average residual stress of the outer ring was -264 MPa，the compressive resddual stress was rather higher n the range of 0~50 μm from surface，and the resddual stress was about -15 MPa n the range of 50~600 μm from surface. This kind of resddual stress distribution was beneficial to improve the service life of the bearing outer rings.