A gasket is capable of providing an excellent slidabiity and holding its sealability without applying lubricant and a gasket that can prevent a resin film from being peeled off of a gasket body and prevent the generation of a molding defect such as pinholes. The gasket can be installed slidably in a outer tube of a syringe, including a gasket body and a resin film formed of a material lower in coefficient of friction than a material of the gasket body, which covers at least an outer periphery of the gasket body, in which when a surface roughness of the resin film on the outer tube side is defined as Ra.sub.1 and a surface roughness of the resin film on the gasket body side is defined as Ra.sub.2, a relationship of 1.5 Ra.sub.1.ltoreq.Ra.sub.2 is satisfied.