In his thesis, the structure and properties of PA6/nanoclay composite fibers were investigated. For this purpose, amino acid (isoleucine) modified and natural clay were melt-blended with nylon6 using a twin screw extruder. Composite Fibers with different contents of natural and modified nanoclay particles (0, 0.5 and 1 percent nanoclay) were produced by a melt spinning apparatus. The structure and properties of the composite fibers were investigated using different techniques such as mechanical analysis, birefringence measurements, Wide Angle X-ray Diffraction (WAXD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscope (FESEM) and Thermal Gravimetric Analysis (TGA). In the X-ray diffraction patterns, the modified nanoclay layers peak at 2?=6.9 ? was shifted to 2?=4.3 ? for the composite PA6/modified nanoclay fibers. This means that in PA6/modified nanoclay composite fibers polymer molecules were penetrated into nanoclay layers and the distance between nanoclay layers was increased. There was also an increase in relative crystallinity of 1% modified composite fibers to 62 percent in comparison to pure nylon fibers with the relative crystallinity of 38%. XRD results also showed an increased in overall crystallinity of composites fibers compared to pure nylon6 fibers. An increase in ? phase crystals was also observed which indicates that nanoclay particles acted as nucleating agents. FESEM observations showed that the amino acid modified nanocaly particles were uniformly distributed at the surface of composite fibers as compared to natural clay. Therefore it seems that the compatibility of the nylon polymer and nanoclay particles has been increased due to the amino acid modification of nanoclays. FTIR spectrograms of composite fibers showed that no new peak has been added and this means that the nanoclay particles had a physical links with the polymer molecules. Birefringence of composite fibers (both modified and natural nanoclays) was increased in comparision to pure nylon fibers and this means that the molecular orientation of the composite fibers has been increased due to the addition of nanoclay particles. Tenacity and elongation at break of the composite fibers were lower than those of pure PA6 fibers. The decrease in mechanical properties was higher for the modified composite fibers compared to natural nanoclay composite fibers. TGA measurements showed that with increase in modified nanoclay content, the onset of degradation temperature was decreased. This means that the polymer molecules were penetrated between nonoclay layers. There was also an increase in weight percentage of residual carbon due to the increase in concentration of modified nanoclay from 0.5% to 1% therefore it can be deduced that the thermal stability of the composite fibers have been improved due to the addition of modified nanoclay particles. Key Words: nanocomposites, bioactive nanoclay, Nylon6, fibers