A one way valve is revealed. The one way valve includes a valve seat and a valve member supported by the valve seat. A hole is mounted at a center of the valve base while an outer circular base is disposed around the hole and an inner circular base is arranged at a center of the hole. The inner circular base has a circular sidewall around an opening. At least one gap is radially formed on the circular sidewall and the gap is vertically penetrating the circular sidewall. The valve member consists of a membrane portion and a rod portion extended from one side of the membrane portion. Thereby the rod portion is passed through the gap of the inner circular base to be set into the opening of the inner circular base.