To provide a valve body and a valve seat of a valve system which show no anisotropy in a contraction ratio at the time of molding, sufficient self-lubricancy, excellent abrasion resistance on sliding surfaces, hard-to damage even if the foreign materials infiltrate between their sliding contact surface, and excellent water tightness for long-time continuous use.

A valve body 7 is superposed on a valve seat 5 having a valve hole 6. The valve body 7 is slid against the valve seat 5 for opening and closing the valve hole 6. In such a valve system, at least one of the valve seat 5 and the valve body 7 is made of underwater slidable resin component which is prepared by adding glass carbon with means grain diameter 3 to 30 micrometers by 40 to 165 parts by weight, preferably fluorine contained resin powder such as tetrafluoroethylene resin by 1 to 30 parts by weight, to polycyano aryl ether resin 100 parts by weight.