With massive trials, spheroidized by austeniting at 810°C and cooling by 1°C/min, a 1.6C (pct) Ultra-high Carbon Steel shows a microstructure of uniformly distributed fine carbides in the ultra-fine ferrite matrix. The grain size of ferrite matrix and spheroidized carbides are about 5um and 0.1～2um, respectively. Further investigation by TEM shows that much dislocation together with twins is obtained for the UHCS, and generally finer grains have higher dislocation density. The spheroidized steel exhibits high tensile strength of 910 MPa and high yielding strength of 653 MPa at room temperature, together with excellent elongation of 18.3%, which shows the UHCS can entirely satisfy certain grades of engineering materials and means the steel may substitute present engineering steel considering lower cost. Furthermore, the steel owns good high-temperature superplasticity, the elongation of 216% obtained at 800°C under a strain rate of 2.5×10-4. Initial analysis suggests that the superplastic deformation mechanics of the steel is grain boundary sliding and grain rotating (GBSR), coordinated by migration of dislocation.