A sensor bearing unit includes a bearing having a first ring and a second ring, and an impulse ring provided with a target holder, with a target mounted on the target holder, and with a sleeve secured to the first ring, the target holder being axially mounted between a lateral face of the first ring and the sleeve. The first ring having at least one anti-rotation feature cooperating with at least one complementary anti-rotation feature formed on the impulse ring so as to prevent angular movement of the impulse ring relative to the first ring.