The present disclosure provides a carbon steel composition for a reduced thermal strain steering rack bar and a method for manufacturing the carbon steel composition. The carbon steel composition for a steering rack bar includes: iron (Fe) as a main component, about 0.39 to 0.43 wt % of carbon (C), approximately 0.15 to 0.35 wt % of silicon (Si), approximately 0.90 to 1.10 wt % of manganese (Mn), approximately 0.02 to 0.04 wt % of niobium (Nb), and approximately 0.10 to 0.15 wt % of vanadium (V). The method for manufacturing a carbon steel composition for a steering rack bar includes: filling and drawing the carbon steel composition; broaching the filled and drawn carbon steel composition; performing nitriding heat-treatment on a surface of the broached carbon steel composition; and inspecting the nitriding heat-treated carbon steel composition.