A retractable bicycle cross bar adaptor, comprising: a bar having a first tube , a second tube and a control unit , the first tube having a first end and a second end, the second tube having a first end and a second end, the control unit connected between the first tube and the second tube , a first hook connected to the second end of the first tube , a second hook connected to the second end of the second tube ; a first connection end formed to the first end of the first tube , a second connection end formed to the first end of the second tube , the second connection end slidably inserted into the first connection end , and characterized by the control unit including a first part and a second part , the first part being a tubular part and having a head formed to a first end of the first part , outer threads formed to an outer surface of the first part , multiple plates extending from a second end of the first parts , the first part including a passage defined axially therethrough, multiple slots formed alternatively between the multiple plates , the first connection end inserted into the first part from the head of the first part and secured to the head of the first part , the second connection end inserted into the first part from the second end of the first part and movably inserted into the first connection end , each of the plates having an tapered outer face along an axial direction of the plate, the second part rotatably and movably mounted to the first part , the second part pressing the plates to clamp the second tube , or the second part releasing the plates so that the second tube is movable relative to the first tube . a bar having a first tube , a second tube and a control unit , the first tube having a first end and a second end, the second tube having a first end and a second end, the control unit connected between the first tube and the second tube , a first hook connected to the second end of the first tube , a second hook connected to the second end of the second tube ; a first connection end formed to the first end of the first tube , a second connection end formed to the first end of the second tube , the second connection end slidably inserted into the first connection end , and characterized by the control unit including a first part and a second part , the first part being a tubular part and having a head formed to a first end of the first part , outer threads formed to an outer surface of the first part , multiple plates extending from a second end of the first parts , the first part including a passage defined axially therethrough, multiple slots formed alternatively between the multiple plates , the first connection end inserted into the first part from the head of the first part and secured to the head of the first part , the second connection end inserted into the first part from the second end of the first part and movably inserted into the first connection end , each of the plates having an tapered outer face along an axial direction of the plate, the second part rotatably and movably mounted to the first part , the second part pressing the plates to clamp the second tube , or the second part releasing the plates so that the second tube is movable relative to the first tube . <EOS>