Abstract: A slidable throttle valve assembly for a carburetor comprising a carburetor body with an intake passage therein, a slidable throttle valve movable across the intake passage, and a throttle valve guide tube connected to the carburetor body and guidably supporting the slidable throttle valve. The carburetor body has guide grooves for guiding the slidable throttle valve which are respectively provided in the body at opposite sides of the intake passage so as to be continuous with the throttle valve guide tube. The throttle valve and guide grooves are of part-circular, cross-sectional shape so that the throttle valve and guide grooves come into contact with each other respectively along lines extending in the sliding direction of the slidable throttle valve downstream of the intake passage.