The invention discloses a foldable packaging box body and a foldable packaging box. The foldable packaging box body comprises a box main body; the box main body comprises a bottom board, and further comprises a first side board, a second side board, a third side board and a fourth side board which are sequentially connected along the periphery of the bottom board in a foldable mode; the first sideboard, the second side board, the third side board, the fourth side board and the bottom board can form a containing cavity with an opening; the containing cavity is used for storing expressed items;a connection board is connected between the two adjacent ends in the first side board and the second side board in a foldable mode, and/or, a connection board is connected between the two adjacent ends in the first side board and the fourth side board in a foldable mode; the end, away from the first side board, of the second side board is connected with a first supporting board in a foldable mode, and/or, the end, away from the first side board, of the fourth side board is connected with a first supporting board in a foldable mode; and the end, away from the second side board or the fourth side board connected with the first supporting board, of the first supporting board is a free end. The foldable packaging box body and the foldable packaging box can reduce the size of the packaging boxbody.