A hydrophilic hyperbranched poly(amido amine) (PAMAM) was successfully bonded onto the active PA-layer of a RO-membrane by chemical coupling. The coating is accomplished by spraying a 10 wt% solution of PAMAM directly after the interfacial polymerisation onto the surface. The chemical structure and performance of both unmodified and modified membranes were evaluated. Results from XPS, SEM and zeta-potential measurements confirmed a successful and stable modification. A model reaction of trimesoyl chloride with butylamine in aqueous and alcoholic solution approved a high possibility for covalent PAMAM bonding to the surface. Application of an aqueous PAMAM solution resulted in an almost complete surface coverage with PAMAM, while the use of a methanolic solution led to an inhomogeneous coverage with PAMAM clusters. The permeability increased by 2025% upon modification with PAMAM. While the modification with the aqueous solution has no negative effect on salt retention, modification with the methanolic solution resulted in lower salt retention. Furthermore, membranes modified with aqueous PAMAM solution showed very low protein adsorption compared to unmodified samples or samples modified with methanolic PAMAM solution. (C) 2014 Elsevier B.V. All rights reserved.