To produce a mock yarn which is similar in appearance to a true yarn with respect to the ability to discern the components of the mock yarn after the twist has been imparted to the mock yarn, the rovings or slubbings forming the mock yarn, after drafting separately but parallel to one another in a drafting frame, are subjected separately to condensing and compaction by suction rollers or belts provided with rows of perforations. Thus compacted and condensed rovings are then combined, twisted and wound up as mock yarns. A core thread can be introduced into each roving or into at least one of the rovings upstream of the last pair of drafting rolls or immediately upstream of the condensing unit for a core mock yarn.