A fluid flow control valve assembly which comprises a valve housing having defined therein a valve chamber defined therein a valve hole, inflow and outflow ports adapted to be communicated with each other through the valve chamber by way of the valve hole; and a valve rod inserted exteriorly of the housing and into the valve chamber and coupled with a handle for turning the valve rod about a longitudinal axis thereof thereby to move the valve rod in a direction coaxial with the longitudinal axis of the valve rod to adjust an opening of the valve hole. The valve rod includes a valve member formed on one end of the valve rod confronting the valve chamber and axially movably inserted in the valve hole, and a shank portion formed on a generally intermediate portion of the valve rod and slidably, but fluid-tightly sealing the valve chamber. The valve member and the shank portion have respective cross-sectional areas which are equal to each other so that fluid pressure acting on the valve rod tending to move the latter in directions opposite to each other are counterbalanced thereby to avoid an axial thrust which would otherwise act on the valve rod.