In the present work, the size effect of polystyrene (PS) latex bead on the electrochemical and electrocatalytic activity of layer-by-layer {(PS-protein)/PSS}(n) films was investigated systematically. Using PS beads of different diameters as the cores, and adsorbed hemoglobin (Hb) or myoglobin (Mb) on the PS bead surface as the shells, the core-shell PS-protein particles were fabricated. The particles were then assembled into layer-by-layer films on solid surfaces with poly(styrenesulfonate) (PSS), designated as {(PS-protein)/PSS)}(n). UV-vis spectroscopy, quartz crystal rnicrobalance (QCM), and cyclic voltammetry (CV) were used to monitor the growth of {(PS-protein)/PSS)}(n) films. The proteins in the films demonstrated direct electrochemistry and good electrocatalytic properties toward reduction of various substrates, such as O-2, H2O2, trichloroacetic acid (TCA), and NO2-. While the films assembled with larger PS beads loaded larger adsorption amounts of proteins in each bilayer, those films with moderate PS bead size demonstrated higher surface concentration of electroactive proteins. For the electrocatalysis, the {(PS-protein)/PSS)}(n) films with smaller PS beads generally displayed better catalytic activity, especially the catalytic efficiency per unit protein surface concentration. Thus, the electrochemical and electrocatalytic activity of {(PSprotein)/PSS)}(n) films can be tailored not only by controlling the number of bilayers of the layer-by-layer films, but also by choosing the PS latex beads with suitable diameter. (c) 2006 Elsevier B.V. All rights reserved.