A retractable rack includes a connecting part, a holding mount, a first support element, a second support element and a positioning mechanism. The connecting part may detachably attach to a stroller frame. The second support element is retractably mounted on the opposite side of the holding mount and capable of selectively locking in a first position and a second position relative to the first support element. The positioning mechanism is mounted in the holding mount for locking the second support element in the positions. When the second support element is locked in the first position, the retractable rack is capable of supporting and connecting a car seat with a first size, and when the second support element is locked in the second position, the retractable rack is capable of supporting another car seat with a second size to the stroller frame.