Blends of PA 6 with SMA or with 12.5-100% fatty amine (C 18) modified SMA at compositions 95/5-60/40 were studied. Particle size of SMA dispersed in PA 6 matrix was around 0.1 mu m due to in situ compatibilizer formation. The strength and stiffness of the blends were higher and toughness unchanged in comparison with PA 6 values. Microscopic observations confirm that improvement of mechanical properties of PA 6 by addition of brittle SMA is due to plastic deformation of SMA particles that consume significant amounts of deformational energy. This cold drawing is caused by compressive stress evolved by bulk deformation; this stress should exceed the critical brittle-to-ductile fracture mode transition. In the blends studied, cold drawing apparently occurred when the developed stress was lower than the critical one. It is concluded that a very fine phase structure with an apparently strong interface makes the plastic deformation of dispersed SMA easier.