Polyaniline (PANI) nanoparticles were synthesized by enzymatic polymerization of aniline monomers using glucose oxidase (GOx). The influence of aniline and GOx concentrations as well as the duration of the polymerization on the formation of PANI nanoparticles was investigated. The UV/Vis spectra of polymerization solution showed absorption peaks at 325 and 434 nm, which are characteristic for PANI emeraldine base. The increase of absorption at 434 nm was exploited for the monitoring of PANI formation. The most optimal duration for the formation of PANI nanoparticles was in the frame of 100-115 h. Extension of the polymerization time does not increased the efficiency of here proposed polymerization procedure. The highest rate of PANI nanoparticle formation was observed in solution containing 0.50 mol L-1 of aniline and 0.75 mg mL(-1) of GOx. Hydrodynamic diameter of synthesized PANI nanoparticles was evaluated using dynamic light scattering technique. Hydrodynamic radius of formed GOx/PANI-nanoparticles increased from 15.8 nm up to 142 nm by prolongation of polymerization process. Synthesized PANI nanoparticles were characterized by cyclic voltammetry and two oxidation peaks at +0.51 and +0.68 V were observed in cyclic voltammograms. These peaks are attributed to emeraldine form of PANI. (C) 2017 Elsevier Ltd. All rights reserved.