The superplasticity and microstructure of the spray formed 1.25C-3.0Si-1.5Cr ultra-high carbon steels (UHCS) are described. The 1.25C-3.0Si-1.5Cr steel processed by spray forming to break up carbide network had microstructure consisting of fine pearlite with average interlamellar spacing of 0.20 mum, and revealed superplastic characteristics at elevated temperature. The dramatic change of microstructure from a fine lamellar mixture to equiaxed grains stabilized by spheroidized particles during superplastic deformation has been observed. The ultimate tensile strength and the pearlite spacing in the 1.25C-3.0Si-1.5Cr steel can be related by the Hall-Petch equation. The estimation on the basis of thermodynamics shows that the content of chromium of 1.6 wt.% is needed to inhibit graphite formation in the 1.25C-3.0Si-1.5Cr UHCS.