A low gel content poly (styrene-ran-butadiene)/poly (methyl methacrylate) (SBR/PMMA) core/shell particles dispersed in a good solvent for the shell was wet spun into a coagulation bath at room temperature. The SEM micrographs of as spun fibers showed various surface topographies and fiber diameters, ranging from 4.2 up to 20 mum depend upon the draw ratio. The osmium tetroxide stained cross-section of fibers observed by transmission electron microscope (TEM), indicated a heterogeneous morphology consisting of dark cores and fairly light shells, which is a result of self-stratification to an overall core/shell morphology in fiber cross-section. The inner core consisted of higher concentration of copolymers with double bonds, while the outer shell is made mainly of ungrafted PMMA chains. The equilibrium thermodynamic analysis based on minimization of surface free energy predicts a predominant core/shell structure which the SBR chains are encapsulated mainly by ungrafted PMMA homopolymers and SBR-g-PNIMA copolymers which agrees quite well with the observed morphology. (C) 2003 Published by Elsevier Science Ltd.