Rotating compensator spectroscopic ellipsometry was used to study the optical properties of a rubbed polyimide layer. Two operating modes in the transmission configuration were studied. One was a conventional mode of `polarizer–sample–rotating compensator–analyzer'. The other was a dual rotation mode of `polarizer–rotating sample–rotating compensator–analyzer'. We found that calibration is not possible in the conventional mode due to the extremely small retardance and non-dichroic nature of the sample. Meanwhile, in dual rotation mode which we developed, a retardance smaller than 0.5° could be measured without calibration. Using this technique, the variation in retardance with rubbing could be easily determined over a range of 320–800 nm. The optical axis could also be determined with high precision for this sample, and this optical axis was found to be parallel to the direction of rubbing.