Optical thin films of three rod-like polymers, a rigid-rod polymer poly(p-phenylene benzobisthiazole) (PBZT), a diadamantane-substituted PBZT (DMT-PBZT) and a bicyclo[2.2.2]octane-substituted PBZT (BCO-PBZT), at different thicknesses were prepared with the solid-state coagulation process. In contrast to PBZT, DMT-PBZT and BCO-PBZT do not have a pi-conjugated backbone because of their aliphatic DMT and BCO moieties. The PBZT thin films showed an out-of-plane optical attenuation coefficient (alpha(0)) of 1300 dB cm(-1) at 600 nm wavelength while the alpha(0) value of the DMT-PBZT and the BCO-PBZT thin films at 600 nm wavelength could not be determined due to their weak absorption in the visible light region. However, the in-plane optical attenuation coefficient (alpha(1)) of the BCO-PBZT thin films was determined to be about 11.4 dB cm(-1) by waveguide measurement at 632 nm. By comparing the optical transmission of the PBZT thin films to that of the DMT-PBZT and the BCO-PBZT thin films, it is concluded that the optical loss in the PBZT thin films is mainly due to intrinsic absorption of the polymer.