The gear components in the aero-engine transmission system are subjected to very high stresses during service at elevated temperatures. Due to requirements of increasing power take-off and weight reduction further improvements in the high-strength gear steel are needed. The aim of this project was to design a new steel composition to give an increase in the core strength by 10 % compared to the currently used BS S 156 high-strength gear steel and increase the material capability to withstand higher operating temperatures of up to 300 oc. In addition to this, it was required that the new steel should also have similar or higher ductility, fracture and impact toughness, fatigue and wear resistance to the current steel, with minimal changes being allowed to the current heat treatment schedule. A final requirement was that the design process should also consider minimising the cost of the new steel composition through reducing the use of expensive alloying elements.