Abstract: A joint for foldable ladder including a hollow disk body having a hollow leg which connects the hollow disk body to the ladder and a number of circumferential cutouts for setting a pre-determined angle of the ladder; a casing having a circular part which rotatably encases the hollow disk body and a hollow leg which connects the ladder, the circular part including two spaced apart circular plates which encase and rotatably engage with the hollow disk body, and the hollow leg including a slot at each surface; a trigger pivotally provided on a lateral side of the casing; an arcuate seat provided within the casing; and a lock piece movable along the casing with respect to the slot of the casing and which is fixed on the arcuate seat at one end and is fixed on the casing at the other end.