Microporous hollow fiber membranes covalently modified with protein ligands offer the possibility of high speed affinity isolation of biologicals. Although using coordination chemistries developed for chromatographic bead separations, affinity membranes are not mass transfer rate limited. A problem in their preparation is that mechanically stable microporous fibers do not, generally, contain functional groups suitable for linking the ligands. This paper presents a method for depositing and cross-linking a chitosan film on the surface of partially sulfonated poly (ethersulfone) hollow fibers. The amine and hydroxyl groups of the coating are further modified to link ligands. Results are presented in terms of equilibrium and dynamic capacities of IgG captured by immobilized recombinant protein A.