​In this work we have investigated the optical properties of thin film camphor sulfonic acid doped polyaniline/poly(methylmethacrylate) (PAni-CSA/PMMA) blend using spectroscopic ellipsometer. The optical constants for the chemically prepared PAni-CSA show amorphous-like characteristics, which can be modeled using Cauchy parametric formula with linear absorption or Tauc-Lorentz formula. The optical constants of the (PAni-CSA/PMMA) blend film were obtained using Bruggeman effective medium approximation (EMA) formula. The results show that the refractive index of the blend system can be adjusted in the spectral range 300–550 nm by controlling the PAni-CSA percentage contained in the film. The blend film is transparent and the absorption coefficient varies linearly with the concentration of PAni-CSA. The system can be used as a adjustable optical constants buffer layer in the hole injection electrode for …​