A time-resolved study of uniaxial deformation processes of semi-crystalline poly(ethylene furanoate) (PEF) at 200 ℃ was carried out using synchrotron simultaneous wide- and small-angle X-ray scattering (WAXS/SAXS) techniques. The stretching was able to dissociate existing lamellar crystal assemblies in the early stages of stretching (for strains less than ∼0.6), causing a slight decrease of crystallinity, and an increase of inter-lamellar distance. As stretching proceeded, an increase of crystallinity and at the same time a decrease of inter-lamellar distance was observed. Preferred orientation behavior in the early stages of stretching was complex, but could be approximated using oblique b-axis orientation associated with intra-lamellar slip along the (100) plane. In the late stages of deformation, new lamellar crystals were formed with their normal, i.e., the c-axis direction, parallel to the stretching direction.