The embodiments herein relate to a benzoxazine resin composition, a prepreg, and a carbon fiber-reinforced composite material. More specifically, the embodiments herein relate to a benzoxazine resin composition that provides a carbon fiber-reinforced composite material that is suitable for use as a manufacture material due to its superior mechanical strength in extreme use environments, such as high temperature and high moisture, as well as a prepreg, and a carbon fiber-reinforced composite material. An embodiment comprises a benzoxazine resin composition having a multifunctional benzoxazine resin; a multifunctional epoxy resin that is a liquid at 40° C. and has three or more glycidyl groups; a sulfonate ester; and optionally at least one thermoplastic resin. The resin may include an interpenetrating network structure after curing.