This document presents a study on the optical absorption properties of polyaniline thin films prepared by the chemical bath deposition method. Key points: 1. Polyaniline thin films were prepared on glass substrates by immersing the substrates in a polyaniline/DMSO solution at 50°C for varying durations. 2. UV-visible absorption spectroscopy was used to analyze the absorption bands and estimate the optical band gap of the films. 3. The band gap was estimated to be approximately 2.5 eV for films prepared at different deposition times and after heat treatment.