An open-end spinning unit has a housing having a cylindrical space, with a complementary cylindrical fiber-opening roller disposed in that space which communicates with a dust removing chamber having a dust separating zone and a dust discharge promoting zone, said zones being connected together through an intermediate passage positioned on the downstream side of a dust removing opening communicating with said space, a wall portion of the casing defining a downstream side of the dust separating zone being comprized by an inclined wall which faces an end portion of a partition separating said zones, the partition having an end wall which is inclined with respect to the vertical direction at an angle equal to or smaller than an angle of inclination of the inclined wall.