Investigated in the present study are the physical properties, morphology, and structure of PP/N6 alloy filaments (10, 20 wt % N6) made with or without PP-g-MAH as compatibilizer. The alloy filaments produced at the take-up speeds of 300 and 800 m/min were drawn with draw ratio of 3.5 and 2, respectively. Stress-strain curves of PP and alloy filaments show ductile and brittle behavior, respectively. It is suggested that the brittle behavior of alloy filaments is due to the presence of microvoids or micropores at the interface of PP and N6; these lead to stress concentration and thus to a decrease in tenacity, modulus, and elongation at break. Effects of the blending of N6 with PP on birefringence and crystalline and amorphous orientation factors of the composite filaments are studied. The amorphous orientation factor, f(am), of PP was found to increase with an increase in the amount of N6. The alloy filaments behaved like isostrain materials and most of the force in spinning and drawing was born by the PP phase. The presence of N6 fibrils helped to orient PP chain molecules in amorphous regions. However, the crystalline factor, f(c), of PP decreased with the increase in nylon fraction. This means the presence of the crystals of N6 caused a decrease in the orientation of the PP crystals. LSCM micrographs of the filament showed the presence of matrix-fibril morphology with the N6 fibrils oriented along the axis. (c) 2005 Wiley Periodicals, Inc.