Low dose (10(-4) - 10(-2) dpa) irradiation of high-purity (99.99%) copper single crystals were performed in the PIREX facility with 600 MeV protons at room temperature. The irradiation hardening effects are investigated by measuring the yield stress or critical resolved shear stress changes and the irradiation induced defect microstructure has been observed under transmission electron microscopy. The variations of the yield stress and defect density as a function of the irradiation fluence are comparable to the existing data from neutron irradiations at similar fluence.