Abstract: The NiO/NiFe bilayers were fabricated with DC magnetron sputtering. Keeping the thickness of the NiFe layers constant at 20nm, it was found that the as-deposited bilayers of NiO(70nm)/NiFe(20nm) showed fairly good unidirectional anisotropy. The exchange field could be as large as 30 Oe although there was no magnetic field to induce an unidirectional anisotropy. The changes of the exchange fields with the thickness of NiO layers, the partial pressure of Ar and the ratio of Ar/O₂ were observed. The mechanisms of these changes were discussed.