A bearing assembly with a sensor, comprising: a rolling bearing whose outer race 2 is mounted on a stationary member; a spring member; and a sensor holder (7, 101, 201, 210) that is made of a synthetic resin and carries the sensor, the sensor holder (7, 101, 201, 210) including a positioning portion fitted onto a radially inner surface of the outer race from a first axial side thereof, the positioning portion including a rib fitted in a circumferential groove formed in the radially inner surface of the outer race, and the sensor holder (7, 101, 201, 210) being an annular member having ends and being supported on the outer race by fitting the positioning portion, wherein with the sensor holder (7, 101, 201, 210) supported on the outer race, the said spring member being mounted in a compressed state so that the sensor holder (7, 101, 201, 210) is strongly fixed in position by elastic recovery of the spring member, and wherein the spring member is an annular member having ends and fitted in an annular groove (14, 102, 203, 211) formed in the sensor holder (7, 101, 201, 210) to extend between the opposite ends of the sensor holder (7, 101, 201, 210), characterized in that the spring member includes a main portion fitted in the annular groove (14, 102, 203, 211), and opposite end portions circumferentially protruding from the annular groove (14, 102, 203, 211), the opposite end portions of the spring member being deflected by abutting each other when the main portion is fitted in the annular groove (14, 102, 203, 211), whereby spring forces by which the sensor holder (7, 101, 201, 210) is strongly fixed in position are increased by elastic recovery of the deflected opposite end portions. a rolling bearing whose outer race 2 is mounted on a stationary member; a spring member; and a sensor holder (7, 101, 201, 210) that is made of a synthetic resin and carries the sensor, the sensor holder (7, 101, 201, 210) including a positioning portion fitted onto a radially inner surface of the outer race from a first axial side thereof, the positioning portion including a rib fitted in a circumferential groove formed in the radially inner surface of the outer race, and the sensor holder (7, 101, 201, 210) being an annular member having ends and being supported on the outer race by fitting the positioning portion, wherein with the sensor holder (7, 101, 201, 210) supported on the outer race, the said spring member being mounted in a compressed state so that the sensor holder (7, 101, 201, 210) is strongly fixed in position by elastic recovery of the spring member, and wherein the spring member is an annular member having ends and fitted in an annular groove (14, 102, 203, 211) formed in the sensor holder (7, 101, 201, 210) to extend between the opposite ends of the sensor holder (7, 101, 201, 210), characterized in that the spring member includes a main portion fitted in the annular groove (14, 102, 203, 211), and opposite end portions circumferentially protruding from the annular groove (14, 102, 203, 211), the opposite end portions of the spring member being deflected by abutting each other when the main portion is fitted in the annular groove (14, 102, 203, 211), whereby spring forces by which the sensor holder (7, 101, 201, 210) is strongly fixed in position are increased by elastic recovery of the deflected opposite end portions.