A foldable baby trailer formed of a bottom frame unit, a trailer bar, a rear upright frame, a handle frame, and a folding control mechanism, two side frame bars and a stretcher frame is disclosed. The stretcher frame that supports a fabric seat panel for the sitting of a baby is held in a sloping position with the transverse front tube thereof spaced above the bottom frame unit at a distance so that when a baby is sitting on the fabric seat panel, the legs of the baby will not touch the ground, avoiding an accident and assuring high level of safety. When turning the handle frame backwardly downwards after pressed the operating button of the folding control mechanism, the foldable baby trailer is collapsed, saving storage space.