To provide a foldable assembly coffin which prevents a body fluid from leaking from a dead body.

A foldable assembly coffin A is composed of: a bottom plate 1; a side plate 2 and 3 mounted to both long sides of the bottom plate 1; a front plate 4 and a rear plate attached to both ends in a longitudinal direction; and a top plate 6. To the bottom plate 1, reinforcing members 11 and 11a are fixed in a liquid-tight manner along both long edges, and an end rail 12 is fixed to the outer end face of the bottom plate 1. On the upper surface of the bottom plate 1, a waterproof sheet 8 is laid so as to cover the inner surfaces of the reinforcing members 11 and 11a at both side portions thereof. In the side plates 2 and 3, either or both of the side plates 2 and 3 are attached to the reinforcing members 11 and 11a with two-folded hinges (7) so that one side plate 2 can be superposed on the upper surface 10 of the bottom plate 1 when the side plate 2 is laid down and the other side plate 3 can be superposed on the side plate 2 and folded while a height is made different from that of the side plate 2.