Exchange bias effects were studied in the simple perovskite NdMnO 3. Nd 3+ ordering is induced by the Mn 3+ ferromagnetic component, and they are antiferromagnetically coupled with each other. At 30 K, both negative and positive exchange bias effects are found, which are dependent on the cooling field. The exchange bias fields are around -2400 Oe and 1800 Oe, respectively. Positive and negative exchange bias effects were also observed at 8 K, but the exchange bias fields are only 130 Oe and -120 Oe. The coupling intensity between Nd 3+ ordering and Mn 3+ ordering, and their initial states determine the polarity of the exchange bias fields. © 2012 American Institute of Physics.