A foldable chair includes a support unit, a fold unit and a seat unit. The support unit includes a main stick having a positioning groove. The fold unit includes a connecting member connected to the main stick and an upper slider assembly movable along the main stick. The seat unit is connected to the upper slider assembly. The upper slider assembly is operable to engage the positioning groove for preventing the fold unit from converting between an unfolded state and a folded state, and to be disengaged from the positioning groove so as to permit the fold unit to convert between the unfolded and folded states.