The present invention relates to a positioning device in sewing machines for closing the toe of socks or the like. The device comprises a pair of laminae (2a,2b) which are arranged mutually adjacent so as to define, between them, a passage (3) in which a portion (11) of the sock, which is arranged proximate to the toe of the sock and is thinner at least with respect to a border (10) which delimits this portion on the sock body side, is inserted. The sock is arranged between the laminae so that one free end (12) of the toe to be closed protrudes from one side of the pair of laminae and so that the body (4a) of the sock protrudes from the opposite side. The device comprises tension application means (14a,14b) which can engage the free end of the toe and cooperate with the laminae in order to position the border, which delimits the thinner portion on the sock body side, against the side (23) of the laminae which is directed toward the sock body during the advancement of the sock along the passage.