<;P>;PROBLEM TO BE SOLVED: To impart excellent performance to a medical rubber stopper such as a rubber plug used in an infusion bag. <;P>;SOLUTION: This medical rubber stopper is formed of composition obtained by mixing 160-200 pts.mass softening agent and 15-40 pts.mass polypropylene with 100 pts.mass styrene-ethylene butylene-styrene block copolymer. The medical rubber stopper formed of the above composition has good moldability, facilitates piercing of a needle, prevents leakage of liquid when the needle is pulled out of the rubber stopper, and further has excellent performance so that the needle pierced through the rubber stopper is hardly pulled out. <;P>;COPYRIGHT: (C)2011,JPO&INPIT