A stackable storage box includes an upper box body and at least one modular storage unit. The upper box body includes a box bottom having a rotary portion and a positioning portion. The modular storage unit includes a lower base, an upper base and a drawer. The lower base includes a lower rotary portion and a lower positioning portion. The upper base includes an upper rotary portion and an upper positioning portion. The upper rotary portion is rotatably coupled with the rotary portion of the upper box body. The upper positioning portion is coupled with the positioning portion of the upper box body for positioning when the modular storage unit relative to the upper box body is rotated by a specific angle. A plurality of modular storage units can be rotatably stacked relative to one another and positioned with the upper and lower positioning portions combined.