Carbon nanotubes (CNTs) have been proposed as a promising material to enhance the interface between electrodes and neuronal tissue. It has been demonstrated that nanostructured carbon surfaces have the potential to dramatically improve the recording and stimulation conditions making it an interesting candidate for electrodes in neural implants. Impedance reduction and high-charge injection are only two advantages that should be mentioned here. But when it comes to in vivo applications, other aspects like reliability and long-term stability play an important role, too. Up to now, not much attention has been paid to these issues. Therefore, we focus in this work on the characterization of CNT-coated microelectrodes for neuronal recordings and stimulation, and special attention will be turned to the mechanical stability and the reliability of the nanostructured carbon surfaces. A simple and efficient fabrication process for multi-walled CNT microelectrodes deposited from dispersion is applied in a microelectrode array (MEA) configuration. To investigate impedance reduction, electrode properties are measured by electrochemical impedance spectroscopy and cyclic voltammetry. As expected, nanostructured electrodes show superior electrical characteristics compared to planar gold electrodes. The impedance of the microelectrodes is reduced by a factor of up to 61, and the DC-capacitance is increased by a factor of more than 1,500. Biocompatibility of the proposed device is validated by neuronal cell cultures. Neural activity (action potentials) can be detected after about 2 weeks in vitro using the CNT electrodes. Furthermore, systematic studies of the electrodes’ stability reveal that even after ultrasonic treatment and after 4 weeks in vitro, the electrical characteristics do not change significantly.