A bottle stress analysis system using polarized light for determining stress levels of a transparent plastic bottle includes a rotation assembly for rotating the bottle. A polarized light source assembly is insertible into the bottle cavity to direct plane polarized light through the bottle wall and an analyzer assembly is positioned outside the bottle for measuring intensity of light passing through the bottle wall. In order to measure changes in polarization, the analyzer assembly has a polarization analyzer positioned to transmit the light to a photodetector. A mechanism for rotating either the polarized light source or the analyzer to determine maximum and minimum polarized light intensity at the photodetector facilitates determination of stress at a plurality of points along the bottle wall. A computer controlled analysis of the polarized light intensity can be used to produce a stress profile of the bottle, permitting rejection of bottles having abnormal internal stress that are likely to fail under internal pressure loading.