We demonstrate that on-line X-ray characterization during fiber processing can be carried out using a low-power X-ray generator and an image plate detector. Two fiber processes using 66-nylon were chosen as examples : high-temperature drawing at different ratios (3.5-5.0 X) and melt spinning at moderate speeds (450 and 1,200 mpm). For the draw measurement, useful diffraction images were obtained in a reasonable time frame (30 min). These patterns were equal in quality to static in-laboratory images and sufficient for quantitative analysis. Results showed significant differences in structure between on-line and off-package samples. The crystal density was found to be lower but the crystal orientation was found to be higher as draw ratio increases. The on-line spinning image was found to be similar to those obtained by synchrotron X-ray measurements, which confirm the development of two-dimensional crystals having a hydrogen bonding characteristic distance during spinning. Finally, several ways to improve the demonstrated on-line setup design will be discussed.