A gasket suitable for a syringe stopping with vacuum is provided. The gasket is compatible with sliding property within the sleeve and water-tightness of the syringe barrel after exiting the sleeve. The gasket 10 includes a gasket body 12 made of a liquid-resistant hard plastic having a tip surface contacting medicinal solution 14 and a concave groove 26 formed on a side surface facing an inner peripheral surface 62 of a syringe barrel 60 and formed continuously to the tip surface contacting medicinal solution； and a sliding contact ring 40 made of an elastic material fitted in the concave groove 26. Then, an outer diameter D1 of a peripheral end 22 of a tip portion 16 including the tip surface contacting medicinal solution 14 of the gasket body 12 is set to be larger than the outer diameter D4 of the sliding contact ring 40
