The invention relates to a positioning device for a withdrawn slide rail, comprising a first sliding member, a second sliding member, a third sliding member and a stopping member, wherein the second sliding member is glidingly connected to the first sliding member and the third sliding member which comprises a pair of third side walls respectively forming a chute; the stopping member is fixedly erected on the first sliding member and comprises a pair of opposite extending wings which are arranged corresponding to the chutes of the third sliding member and respectively provided with a contact surface; and the distance between the contact surfaces is slightly smaller than the distance between the chutes of the third sliding member so that the chutes of the third sliding member respectively contact with and support the contact surfaces to form the friction contact positioning effect.