In this study, optimized conditions were investigated using response surface methodology for the preparation of lysozyme loaded dextran-chitosan nanoparticles. Nanoparticles were prepared using polyelectrolyte complexation method. Relevant factors including polymer ratio, protein concentration, stirring rate, and temperature were considered and the effects of these factors on size, polydispersity index (PDI), entrapment efficiency (EE), and zeta potential of the nanoparticles were investigated. The optimum condition for the nanoparticle preparation was found at chitosan/dextran ratio of 0.37, 1.5 mg/mL with 1600 rpm stirring at 32 °C. The particle size, PDI, encapsulation efficiency, and zeta potential at the optimum conditions were 188.5 nm, 0.287, 84.6 %, and -18.76 mv, respectively. This study revealed that encapsulation of positively charged lysozyme, as a model protein, within negatively charged dextran-chitosan nanocarriers improve the loading capacity and the release properties under physiological conditions.