[en] Highlights: • A facile method is presented to prepare uniform Bi₂O₃ nano-films. • The thickness of the Bi₂O₃ nano-film is readily controlled. • The dispersion mechanism of stable bismuth oxide suspension is proposed. In this work, we prepared uniform Bi₂O₃ nano-films through facile electrophoretic deposition (EPD) based on stable Bi₂O₃ nanoparticle suspension. The suspension was obtained by ball-milling Bi₂O₃ micro-particles in distilled water and employing paper-manufacturing waste sodium lignin sulfonate (MZS) as dispersant. The correlation between the stability of Bi₂O₃ nanoparticle suspension and EPD parameters including electrostatic repulsion, steric hindrance, and attractive van der Waals force was investigated. The thickness of Bi₂O₃ films was controlled by adjusting the voltage and time of EPD. This work opens up the opportunity for bismuth oxide nanoparticles to be assembled efficiently for various applications.