A high carbon steel with ultrafine microduplex structure was successfully produced through equal channel angular pressing (ECAP). According to the morphological characteristics of cementite lamellas in high carbon steel, the deformed pearlite microstructure consists of shear break lamella, locally thinned lamella and irregularly bent lamella. The proportion of locally thinned lamella and irregularly bent lamella has increased with the pass number of ECAP. In addition, the deformed pearlitic ferrite became a supersaturated solid solution of carbon, due to the partial dissolution of cementite during ECAP. The tensile strength (1265 MPa) of the sample after one pass ECAP has increased 1.61 times than as-received (788 MPa). The tensile strength after two pass ECAP was further increased and reached 1291 MPa. The material after ECAP was obtained high strength and good plasticity due to the together effect between solid solution strengthening and the good plasticity of cementite.