Abstract: In a filler neck cap including a screw body and a cap, the cap comprises two members of a cover portion and an annular thin latching member so as to enable different materials, each of which exercise optimumly functions necessary to the respective members. In one example with respect to a combination of preferred materials, the cover portion of the cap and the screw body may be formed from polyacetal resin, but the annular thin latching member interposed therebetween may be formed from polyamide resin; the safety plastic filler neck cap may be manufactured from the combination of these synthetic resins, which is designed to be capable of controlling the screwing torque and of stabilizing the cap dislodgement. According to the present invention, there can be provided the comfortably operable filler neck cap increasing the dimensional stability of the cap and eliminating the grating noise during the cap opening-closing operations.