In order to obtain high-strength materials, several plastic deformation processes are effective. The aim of this study is to obtain high strength material with ductility. To put it definitely, the carbon steels with various carbon contents were deformed by the repetitive side extrusion process and heat treatment, and the properties of materials such as Vickers hardness, tensile strength and microstructure observation were investigated. It was possible to deform by repetitive side extrusion process without any failure for all steels. Vickers hardness was increased a value of 100 comparison to initial hardness for all carbon steels after 1 pass, and hardness increased with increasing number of passes. The microstructures of all steels were refined by deformed structure. After heat treatment, the tensile strength became lower and total elongation increased with decreasing hardness. The uniform elongation of tensile experiments increased with increasing heat treatment time on all materials.