Attractive interactions between negatively charged bovine serum albumin (BSA) at pH 7 and 9 and poly-(sodium acrylate) were obtained by substituting a small fraction of acrylic units with alkylacrylamide units. Using light scattering, equilibrium dialysis, and viscometry, we investigated, in dilute solution, the association between BSA and two sets of modified polyacrylates of mean molecular weight 5000 and 150 000, respectively. The formation of complexes was revealed by pronounced increases of the scattering depending on the hydrophobicity of the synthetic polymer. It was not observed with entirely hydrophilic polyacrylates under the same conditions. In the case of long polyacrylates, the apparent hydrodynamic radius of the complexes was slightly larger than that of the free polymer. The polydispersity in size of the complexes seemed low. In the case of short polyacrylates, the complexation can be depicted as the "adsorption" of several polymer chains per protein. In contrast, complexes with long polyacrylates contain a single chain that accommodates several proteins.