Abstract : This thesis deals with the study of the electrochemical properties of carbon nanotube (CNT) fibers. On the one hand, we have characterized this material as new analytical sensors. With respect to this, a fabrication procedure to obtain stable and reproducible microelectrodes has been elaborated. Their analytical performance has been characterized with and without surface modification in order to emphasize their selectivity. On the other hand, we have studied the electromechanical properties of CNT fibers in the context of electrochemical actuators that can convert electrical into mechanical . The performances has been characterized in term of generated strain and stress. Possible ways of optimization have been investigated. Finally, we demonstrate the influence of the CNT orientation on the fiber properties. This first study on electrochemical properties of CNT fibers opens various promising applications regarding reliable and efficient analytical tools (sensors, biosensors) and mechanical devices (robots, microchirurgical tools, artificial muscle).