A pulser ring for a rotary encoder has a mounting ring (1), a pulsar ring body (2), and a seal ring (3). The mounting ring (1) is made of a non-magnetic material. One end of the mounting ring (1) is fitted into and fixed to an inner ring (202) on the rotation side, and the other end is positioned in proximity to an outer ring (201) on the stationary side with labyrinth-like clearances (G1, G2, G3) present between the mounting ring (1) and the outer ring (201). The pulsar ring body (2) is molded of a synthetic resin material or rubber-like elastic material mixed with magnetic powder, is magnetized in multiple poles, and is integrally installed on the inner surface of the mounting ring (1). The seal ring (3) is disposed on the inside of the mounting ring (1), is fitted into and fixed to the inner ring (202) with the mounting ring (1) disposed therebetween, and is slidably in intimate contact with the outer ring (201). The construction above makes the magnetic field of the pulsar ring less susceptible to disturbances caused by foreign matters, slurry, and an external magnetic field from the outside, and as a result, the pulser ring can maintain a stable magnetic pattern.