Provided herein is a baby stroller, which has an expanded mode and a folded mode, and includes a lower arm set, a connection part, a front wheel frame, a slide block, a rear wheel set, an upper frame, a first link rod set, a handling tube, a supporting rod set, two seat supports, and two second link rods. Due to the couplings between the slide block, the handling tube and the upper frame and the coupling between the slide block and the rear wheel rocker arms, the baby stroller may easily be folded so that it occupies considerably less space, and thereby improve its portability and facilitate its stowage and transportation.