There is provided a valve device for a fuel tank. A housing is provided with a valve chamber and a vent chamber defined via a partition wall. The partition wall is provided with an opening. A float valve is received in the valve chamber to be movable up and down. The float valve includes a lower member and an upper member. The upper member includes a top portion, an outside wall extending from the top portion, and an elastic engaging piece configured to engage with an engaged portion of the lower member. The elastic engaging piece extends from a location on the back surface of the top portion, which is located inward from the outside wall, and is configured to elastically return after being bent in an outward radial direction of the upper member and thus to engage with the engaged portion of the lower member.