Thermally stable, smooth and highly transparent plasma polymerized (N-benzylaniline) thin films are deposited onto glass substrates under ac (50 Hz) glow discharge plasma. Thermal stability and optical absorbance of the films are very high, indicate conjugation in the films, which depends on their thickness. Other optical parameters such as band energy gaps, steepness, Urbach energy, dielectric constant, etc. are also observed to vary with film thickness. The small value of extinction coefficient and high value of refractive index confirms that the films are very smooth highly transparent, and therefore suitable for anti-reflecting coating and infrared applications.