The demand for electrically conductive fibers and textiles structures which are used for industrial materials like sensors, electro-static discharge, electromagnetic interference shielding, data transfer in clothing and for military applications like camouflage technology is growing up. Conductive fibers based on polymers are produced both by coating of non-conductive fibers with a conductive polymer and by wet or melt-spinning of conductive polymers or a compound of conductive and non-conductive polymers. In this thesis polyaniline was synthesized using chemical method. Polypropylene, polyaniline and dodecyl benzene sulfonic acid were melt blended using a twin screw extruder to achieve a homogeneous composition and relevant granules were prepared. Composite filament yarns which contained 1.7wt% and 5wt% polyaniline were produced using a melt spinning aparatus. Mechanical properties of the composite fibers were measured using a tensile strength tester. Morphological properties of the fibers were studied using light and field emission electron microscopy (FESEM). Electrical conductivity of the samples (composite granules, fibers and stretched fibers) were studied. Also to improve the electrical properties of composite granules and fibers containing polypropylene, polyaniline and dodecylbenzene sulfonic acid, the samples were immersed in inorganic hydrochloric and sulfuric acids. In order to investigate the effect of this inorganic acids on the crystallization and thermal behavior of composite fibers, DSC tests were performed. Also, the effect of acid on the samples were analyzed by UV-Vis test. The FESEM images show the melt blending of polypropylene and polyaniline is homogeneous. Tensile strength and modulus of the composite fibers were about 35MPa and 1000MPa, respectively and these data are in the range of the strength and modulus of fibers which are used in the textile industry. Electrical conductivity of the composite granules measured by four-point method was in the range of semiconductor materials. In fact, with the addition of 5% polyaniline to the non-conductive polypropylene with the conductivity of 10 -14 S/cm, the electrical conductivity of the composite granules increased with the order of 10 8 times to about 10 -6 S/cm. The study revealed that with the increasing of draw ratio of the fibers, the conductivity of them is improved. It seems that the conductive paths within the composite fibers expand due to drawing. Inorganic acids dope non-conductive emeraldine base polyaniline particles in the granules (and fibers) and expand conductive polyaniline phase and as a consequence their conductivity increases. Electrical conductivity of hydrochloric acid treated granules was higher than that for sulfuric acid treated ones and this may be due to smaller size (higher mobility) of chloride groups in hydrochloric acid than sulfate groups in sulfuric acid. DSC results showed that acid-treated fibers have lowerr crystallinity than that of non-treated fibers. Therefore, it seems that polyaniline/dodecyl benzene sulfonic acid phase is expanded due to acid treating and phase crystallization of polypropylene is reduced. Also, UV spectroscopy studies showed that in acid treated samples transitional ? ? ?* mutations are higher than those of non-treated samples and this confirms improved electrical conductivity of acid-treated sample fibers. Keywords: polypropylene, polyaniline, mechanical properties, electrical properties