An experimental study is reported on the measurement of polymer melt film thickness in a rotating disk polycondensation reactor. The layer thickness of molten poly(ethylene terephthalate) on a rotating disk was measured at 280°C using an electrical conductivity probe at different radial and angular positions. It was observed that the polymer film thickness was not uniform in both radial and angular positions, particularly for high molecular weight polymers. For the slowly rotating disk system employed in our experimental study, the disk rotational speed and gravity effects on the polymer-layer formation were found to be quite significant. The experimental results were used to develop an empirical correlation for the calculation of polymer film thickness and polymer melt holdup on a rotating disk. © 1995 John Wiley & Sons, Inc.