Poly(2-ethyl-2-oxazoline) (PEOX) formed self-assembled fibers in aqueous solutions above the cloud point temperature (Tc) through a slow crystallization process. The fiber formation above Tc happened both in pure water and in the presence of salting-in (SCN-) and salting-out (CH3COO-) ions. The crystal structure and the melting temperature of the PEOX fibers were determined.