A baby stroller is formed by a stroller frame and a chair, and the stroller frame includes a rotatable base. When the baby stroller is unfolded, the base is provided for abutting the stroller frame and positioned automatically, and when the baby stroller is folded, the chair and the stroller frame are folded and positioned directly together with the rotation of the base. The chair includes a folding joint, such that the chair can be folded directly onto the stroller frame to provide a simple, easy and quick operation and to achieve the effect of reducing the storage volume of the baby stroller.