Abstract: Method of and apparatus for spinning yarn of staple fiber in an air vortex in a spinning tube. Separated fibers are withdrawn from the spinning tube in counterdirection to a whirling flow of air produced in a pneumatic chamber coupled to the spinning tube. The yarn being built is twisted in the pneumatic twisting chamber by means of concentric air streaming producing an excited potential air vortex about the longitudinal axis of said pneumatic twisting chamber and about the yarn passing therethrough.The apparatus is characterized in that a surface of revolution defining the cavity of said chamber is formed by a peripheral surface on which at least one duct opens for supplying pressure air and which merges into lateral surfaces which, beginning from the widest portion of said peripheral surface, converge up to a distance of a gap between an outflow aperture of an outflow tube and an outflow aperture of a yarn take-off tube.