Electroactive polymers (EAPs) include groups of polymers with sensitive dimension or shape by electric field. Among these polymers, conductive polymers such as polyaniline (PANi), polythiophene (PTP) and polypyrrole (PPY) have been studied in many fields like actuators, sensors, batteries, solar cells, capacitors, etc. A typical characteristic property of EAPs is that they will undergo a large amount of deformation while sustaining large forces , making them particularly attractive for use anywhere where a muscle-like response is desirable, including in medical devices, prostheses, toys, etc. The conduction in these polymers is due to the presence of delocalized molecular orbitals. It is limited to direct use of these polymers due to their weak mechanical properties. In attempts to improve mechanical properties, blends of PANi (or the other conducting polymers) with other polymers (such as polyacrylonitrile (pan), polyurethane (PU) and …) have been produced, particularly in form of nanofibers. Nanofibers have suitable mechanical properties and more flexibility because of their high surface to volume ratio. Therefore in this work we investigated the electrochemical characteristics of bundled coaxial pan/ pan- pani nanofibers containing TiO 2 nanoparticles in core, as an actuator. We synthesized polyaniline (emeraldine salt) using aniline hydrochloride, ammonium persulfate and HCl as monomer, oxidant and dopant respectively. The electrical conductivity of the pelletized polymer measured using 4-probe method was about 2 S.cm -1 . In the next step we fabricated aligned core-sheath pan- TiO 2 (0-15%)/ pan- pani nanofibrous bundles through electrospinning process, with an average diameter of 199- 350 nm. Afterward morphological, mechanical and electrochemical properties of nanofibrous bundles were studied. Scanning electron microscopy (SEM) images verify the production of uniform approximately parallel nanofibers with a normal distribution of fibers diameter. Furtheremore from SEM images, it can be observed that with increase of TiO 2 percentage in core, the diameter of nanofibers increases, too. Stress-strain results confirmed the increase of tensile strength of nanofibrous bundles with increasing the amount of TiO 2 nanoparticles in core of nanofibers, but there is a critical limit for TiO 2 percentage. Voltammetry results show that the presence of TiO 2 nanoparticles in nanofibers enhances the electrochemical redox current. As well as, it can be found that the presence of PANi in outer surface of nanofibers show a redox peak near the 0.7 volt and it increases the electrochemical current of bundles significantly whereas the electrochemical redox current of PAN/ PAN- PANi nanofibrous bundles is four times more than neat PAN nanofibrous bundle. Transmission electron microscopy (TEM) image confirms the core-sheath structure of PAN/ PAN-PANi nanofibers. It can be observed in TEM image that a PAN core with average diameter of 53 nm is surrounded by the PAN-PANi sheath with the same diameter. All findings verify the high ability of core- sheath PAN- TiO 2 / PAN- PANi nanofibrous bundles as an electroactive actuator (or artificial muscle). Keywords: Core- sheath nanofibers, electroactive polymers, polyaniline (PANi), TiO 2 nanoparticles, electroactive properties.