Polyethylenimines (PEIs) with different molecular weights [number-average molecular weights (M n 0 s) ¼ 60,000, 1200, and 423] were coupled onto macroporous beads. These rigid and spherical beads were prepared by the crosslinking of 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate. The PEI attachment was carried out through epoxy groups yielded in a previous activation step with epichlorohydrin on matrix hydroxyl groups. Different initial concentrations of PEI were assayed. The supports so obtained were characterized by several techniques (Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury intrusion porosimetry). All of the PEI-containing beads were used to analyze the influence that the molecular weight, the shape of the polycationic ligand (PEI), and the degree of coupling onto the matrices may have had on the efficiency of the retention of the bovine serum albumin protein used as a model biomolecule. In these assays, the PEI-modified beads with M n ¼ 60,000 showed better results than those modified with PEIs with M n 's of 1200 and 423. The presence of sparse and long chains of PEI 60,000 onto the matrix, by reason of their highest accessibility toward the large protein, may have resulted in a better disposition of functional groups, whereas more short chains in the other PEIs (M n 's ¼ 1200 and 423) used as ligands would not have.