We report a nanocarbon film based microdisk array electrode with an extremely stable electrochemical response for measuring serotonin. The nanocarbon film was formed on a silicon substrate with an electron cyclotron resonance sputtering method, and the nanocarbon film based microdisk array electrode was fabricated using photolithography. The array electrode consists of 335 microdisks with a diameter of 10 µm. The center-to-center distance of each microdisk is 100 µm. The electrochemical properties of the nanocarbon film based microdisk array electrode are compared with those of a gold film based array electrode. Before microfabrication, both nanocarbon and gold film electrodes (both 2 mm in diameter) showed steady responses for the continuous voltammetric measurement of 1 µM of serotonin. Moreover, each microdisk array electrode exhibited a sigmoidal response. The obtained current densities were higher than those of conventional sized electrodes owing to the microelectrode effect. However, the current value at 0.45 V vs. Ag/AgCl at the gold film based microdisk array electrode decreased rapidly and fell to 30 % of its initial value after ten potential scans. In contrast, the nanocarbon film based microdisk array electrode decreased only 2 % under the same measurement condition. Despite the fact that there was more than 10 times the current density at the microelectrode, our nanocarbon film showed excellent performance in suppressing serotonin adsorption.