A collapsible storage box contains: a bottom plate, a first long plate, a second long plate, and two foldable short plates. Each foldable short plate includes a first connection sheet and a second connection sheet. A front end of the bottom plate retains with multiple first L-shaped hooks on a bottom of the first long plate, multiple first rotary shafts on a rear end of the bottom plate rotatably connect with multiple first retainers on a bottom of the second long plate respectively, a first side of the bottom plate retains with a first flexible hook on a bottom of the first connection sheet of each foldable short plate, and a second side of the bottom plate retains with a second flexible hook on a bottom of the second connection sheet of each foldable short plate. Thereby, the collapsible storage box is expanded and retracted quickly and easily.