In this thesis, the effect of fiber diameter or specific surface area of fiber on the electrical, thermal, and electromagnetic shielding effectiveness of polypyrrole coated web of fibers/nanofibers was investigated. Results showed that electrical resistivity of polypyrrole coated web of fibers/nanofibers depends on the fiber/nanofiber diameter, applied pressure on the surface of fiber/nanofiber webs, web thickness, and type of fibers/nanofibers. Electrical resistivity of polypyrrole coated web of fibers/nanofibers increased as fiber diameter decreased. Moreover, electrical resistivity of polypyrrole coated web of fibers/nanofibers decreased considerably as applied pressure on the surface of fiber/nanofiber webs and thickness of webs increased. In this work, it was observed that the electrical resistivity is higher for polyester webs than acrylic. The results indicated that heat generation using applied voltage on the polypyrrole coated web of fibers/nanofibers, increased with voltage, time of applied voltage, and fiber diameter. Furthermore, after applying voltage on polypyrrole coated web of fibers/nanofibers, electrical current versus time increased sharply at the first and then showed a marginal increase. The temperature increase of polypyrrole coated web of fibers/nanofibers decrease after removing the applied voltage formed a hysteresis loop. In case of electromagnetic shielding effectiveness of polypyrrole coated web of fibers/nanofibers, it was observed that increase of fiber diameter and decrease of electrical resistivity caused an increase in absorption and a decrease in reflection percentage of electromagnetic radiations in the frequency range of 5 to 8 GHz, respectively. Overall, considering the high specific surface area of the nanofibers, polypyrrole coated web of nanofibers depicted excellent electrical, thermal, and electromagnetic shielding effectiveness.