Polymers bearing quaternized 4-vinylpyridine (QVP) groups are known for their antibacterial activities and these polymers can form polyelectrolyte complexes (PEC) with polyanions through electrostatic interactions. PEC formation can be used to adjust the antibacterial activity of polymers of QVP, deliver active molecules, or design antibacterial supramolecular structures. However, the antibacterial activity of PECs of QVP polymers has not been investigated. In this study, a copolymer of QVP was mixed with polyacrylic acid in various molar ratios of components to form PECs. Hydrodynamic diameters and zeta potentials of formed PECs were determined by dynamic and electrophoretic light scattering spectroscopy techniques. The zeta potentials of PECs changed between -24 and + 16 mV with variation in the ratio of components. Antibacterial assays against E. coli revealed a relation of PEC formation with antibacterial activity since MIC values changed between 125-1000 mu g/mL according to the ratio of components.