To provide a medical rubber cap which is provided with a superior sealing characteristic and which maintains superior coring resistance and re-sealing characteristics even if a syringe needle is applied to the rubber cap multiple times, and to provide its production method.

The surface layer part of a rubber cap is provided with a layer containing fluorine atoms. The composite proportion of the layer containing fluorine atoms is continuously decreased from the surface to the inside of the cap. Preferably, a method of impregnation uses a method for bringing the rubber cap whose surface is purged into contact with an atmosphere containing a fluorine gas.