Antiferromagnetic Co3O4 nanowires with an average diameter of about 8 nm have been synthesized by using the nanocasting route. The nanowires were characterized by powder X-ray diffraction, transmission electron microscopy, and a superconducting quantum interference device magnetometer. The magnetic measurements show a unidirectional exchange anisotropy accompanied by an enhancement of the field-cooled coercivity at low temperature. These effects suggest the presence of an exchange interaction between the antiferromagnetic core and the surface spins. A strong dependence of the exchange field on the magnitude of the cooling field and a training effect have been observed. The dependence of exchange bias field on temperature reveals the important role played by the antiferromagnetic core in the exchange coupling.