The strength properties of fibers made from polyimideamide (PIA) nanocomposite were investigated and the effect of the presence of MMT in the fiber-forming polymer on the porous structure and supermolecular structure of fibers was analyzed. It was found that lower strength properties (tenacity, elongation at break) of PIA nanocomposite fibers, as compared with those ones of fibers without montmorillonite (MMT), are connected with a lower deformability of the poly-mer during drawing stage and the collapse of MMT galleries, confirmed by WAXS investigations. This results in the formation of agglomerates that are weakly connected with the fiber-forming polymer. (c) 2007 Wiley Periodicals, Inc.