In this investigation repetitive upsetting-extrusion (RUE) process was used to investigate the effect of severe plastic deformation on the microstructural changes and flow behavior of commercial pure copper. Initial material together with two passes, four passes and eight passes of RUE in annealed and non-annealed condition were studied. Results show that grain refinement, in the scale of nano meter, has mostly been achieved only after two passes of RUE which is essentially a combination of one upsetting and one extrusion path. Increasing the number of passes after four passes of RUE did not have discernible effect on the grain refinement. Such a behavior is explained to be due to saturation of dislocations and the formation of high angle grain boundaries after only two passes of RUE. The grains after eight passes of RUE process even became slightly larger than the two and the four passes of RUE. This was related to restoration phenomena occurring during high number of passes of RUE. Flow strength of the material after different passes substantially increased, though the rate at which the flow stress increased declined by increasing the number of passes. ETMB model were used to explain the deformation behavior of the RUE samples.