Abstract: The microstructure and mechanical properties of a certain grade of medium carbon steel were investigated systematically in different controlled cooling processes using the ultra fast cooler provided at the finish rolling exit. It was found that such an ultra fast cooling process can restrain the formation of pro-eutectoid ferrite, and destroy its initial network distribution and minimize the laminar spacing of pearlite obviously. The strength of specimens and their impact toughness at room temperature both increase with the decreasing ultra fast cooling temperature. So, implementing the ultra fast cooling process as just ending the high temperature finish rolling can improve greatly the mechanical properties of specimens and avoid the overloading due to low temperature hot rolling so as to improve the rhythm of rolling production.