A float valve device for a fuel tank of an automotive vehicle. The float valve device comprises a valve body installed to an upper wall of the fuel tank. The valve body is formed thereinside with a communication passage for establishing communication between inside and outside of the fuel tank. A valve mouth member is fixedly disposed inside the communication passage and includes a lower end section having a peripheral portion defining thereinside a valve opening which forms part of the communication passage. A float is disposed inside the valve body and movable relative to the valve opening in accordance with a level of the liquid in the fuel tank. A rubber member is securely disposed at an upper section of the float. The rubber member has a sealing face which is substantially flat and contactable with the peripheral portion of the valve mouth member to close the valve opening upon ascending of the float.
