Hydrophilic microfiltration membranes with functional groups that can be used as coupling sites for ligands are of central interest in affinity separation, especially in view of biomedical applications. In this study we investigate covalent coupling of bovine serum albumin (BSA) as model ligand onto cellular-type poly(ethylene vinyl alcohol) (EVAL) microfiltration membranes. EVAL membranes prepared from the ternary water/DMSO/EVAL system are only suitable for activation and coupling reactions in aqueous media. Employing glutaraldehyde (GA) or oxiran to activate the secondary alcohol groups of the vinyl alcohol segments yielded a BSA-immobilization per internal area of 0.1–0.2 μg/cm2 (4–8 mg/g per membrane mass). Preparing microfiltration membranes from the quaternary water/1-octanol/DMSO/EVAL system, using 1-octanol as nonsolvent-additive in the casting solution, enabled to perform surface functionalization reactions in organic media as well as surface activation by a low-pressure glow discharge treatment. 0.3–0.45 μg/cm2 BSA per internal area (16–18 mg/g per membrane mass) was covalently coupled onto the porous membranes by applying trichloro-s-triazine (sTT) or sulfonyl chloride activation reactions, while a BSA-immobilization of 0.5–0.55 μg/cm2 (20–22 mg/g per membrane mass) was reached via plasma activation. To determine the degree of BSA-immobilization, the internal surface area of the membranes prepared was measured by BET. The formation of a BSA-monolayer is assumed on the pore surface as maximum immobilization. Such membranes can function as adsorptive devices for endotoxin removal from blood or blood plasma.