This study aims to determine the effectiveness of adding PANI/tm-ZrO₂ to paint layers in reducing the corrosion rate of ST42 steel. PANI/ZrO₂ has four phases: cubic (c), tetragonal (t), tetragonal-monoclinic (tm), and monoclinic (m). The research focuses on the tetragonal-monoclinic phase with varying compositions of 2.5%, 5%, 7.5%, and 10% mixed into the base paint. The material used is ST-42 steel, commonly utilized in everyday activities. Corrosion rate measurements were conducted using the Tafel Plot method, which evaluates the corrosion rate on the metal surface through electrical current. The results showed that adding PANI/tm-ZrO₂ to the base paint can slow down the corrosion rate, with the STCTM10 sample providing the best protection, achieving a corrosion rate of 0.009412 mpy, compared to the ST-42 substrate's corrosion rate of 1.0055 mpy on the 21st day of testing. The composition of PANI/tm-ZrO₂ also influences the level of corrosion protection, as evidenced by varying corrosion rates: STCTM 2 (2.5%) at 0.05249 mpy, STCTM 5 (5%) at 0.00861 mpy, STCTM 7 (7.5%) at 0.02118 mpy, and STCTM 10 (10%) at 0.009412 mpy.