Abstract: A liquid treatment apparatus which can perform dialysis at a very high efficiency and which is suitable for dialysis of human blood is provided. The apparatus comprises a bundle of a vast plurality of semi-permeable hollow fibers substantially equal in length, which is gathered and bonded only at both end portions thereof. An inside liquid is permitted to flow the interior of the individual hollow fibers. This bundle of hollow fibers is loosely suspended in a vessel having a substantially U-shaped passage for an outside liquid, and the two gathered and bonded portions of the fiber bundle are connected to the vessel at two spaced-apart openings formed on the top face of the vessel. A dialyzate flowing outside the hollow fibers is introduced from an introduction opening formed in the bottom face of the vessel.