A joint structure for a baby stroller comprises a articulated assembly connected to the rear leg tube of the stroller frame, and uses the articulated assembly controllable pivoted with the push bar and the front leg tube. The articulated assembly has an engaging pin for locking the push bar in a fixed position therefore to keep the stroller in a erected position. The engaging pin may pulled and disengaged from the end of the pull bar, and allows the push bar to rotate to collapse the stroller.