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The influence of deep cryogenic treatments (DCT) on the microstructure and properties of a cold rolled Cu-1.34Ni-1.02Co-0.61Si alloy was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), an X-ray diffractometer (XRD), a mechanical testing machine and a low resistance tester. The DCT refined and homogenized the microstructure of the alloy after cold rolling at 30 % reduction. The grain refinement of the alloy became more obvious and the microstructure distribution became more uniform with increasing DCT time. The DCT promoted the precipitation of the solid solution elements Ni, Co and Si from the Cu matrix to form many fine and evenly distributed 0.1?m~1?m spherical and strip second phase particles in the grain and grain boundary. The tensile strength, conductivity and elongation of the alloy before and after cold rolling at 30 % reduction increased with increasing DCT time, and tended to be stable at about 36 h. After DCT for 48 h, the tensile strength, conductivity and elongation of the alloy before and after cold rolling increased by 5.4% and 4.4%, 6.7% and 8.0%, 13.2% and 18.7% respectively. The tensile strength of the alloy after cold rolling was higher than that before cold rolling. The conductivity and elongation of the alloy after cold rolling was lower than that before cold rolling. However, the both differences decreased with increasing DCT time. The dimple quantity and depth of the alloy with DCT were larger, and the dimple distribution was more uniform than those without DCT.