We report optical spectroscopic measurements of plasma-polymerized thin films coated on aluminum (Al) substrates over a spectral range from 0.01 to 6 eV, While the reflectance spectra, R(omega), remain almost unchanged in the infrared range as compared with the bare Al, R(omega) starts to decrease significantly in the higher energy above 2.5 eV. This decrease in R(omega) arises from electronic absorptions characteristic of the polymer films. Moreover, the details of R(omega) in the energy above 3 eV depend on the fabrication conditions of the polymer films. Our results, therefore, demonstrate that this optical measurement can be an excellent method to characterize the quality of polymer films deposited by the plasma polymerization process.