A foldable storage box comprises a soft walled body open at its top end and closed at the opposing end, a top frame being mounted with the walled body and contiguous to the open top end, and a bottom frame being mounted with the walled body and contiguous to the closed opposing end; wherein the top frame are provided with attachment elements respectively on its bottom and side surfaces, the bottom frame are provided with attachment elements respectively on its top and side surfaces, such that separate boxes can be held in stacks or side by side with the attachment elements. A plurality of supporting bars are provided within the walled body to each serve as a support between the top and bottom frames to form a container. The supporting bars can be detached from the both frames to enable the walled body to be folded into a flat pack.