To reduce the number of parts and manufacturing costs as well as to secure sealing performance of a valve member, in an on-vehicle two-stage fuel tank evaporated gas vent valve assembly.

This valve assembly 30 controls ventilation of evaporation gas from a fuel tank to a canister during oil supply. A second vent passage 60 is inserted in a cup-shaped member 42 (a poppet) to be operated by a float 44. The cup-shaped member 42 is movable relatively to a valve member 76 attached to the float 44. During oil supply, ventilation is performed through a vent passage 36 until the poppet closes the first vent passage 36 after the fuel level is raised. After the large-diameter first vent passage 36 is closed, ventilation is performed through the small-diameter second vent passage 60. When a tank is filled, the valve member 76 closes the second ventilation passage 60. Seal lips 72, 74 for closing the first and second vent passages 36, 60 are formed into one piece and integrally formed of flexible sealing materials through an opening of the cup-shaped member 42, to form a seal member 70.