Abstract: The invention relates to a coupling unit for coupling two tubular membrane elements of the kind used in membrane filter technology, forming extensions of one another. The coupling unit comprises a jacket piece which is provided at both its ends with sealing surfaces intended to engage the facing ends of the membrane elements to be coupled thereto. The sealing surfaces may be formed on the interior peripheral wall of the jacket piece to engage the exterior peripheral wall of the ends of the membrane elements. However, the sealing surfaces may also be formed on the cross-cut end surfaces of the jacket piece, and engage the cross cut end walls of the membrane elements. The interior of the jacket piece may comprise an axially extending conduit portion to communicate with corresponding flow conduits in the membrane elements.