Abstract The development of a simple, sensitive, selective, and stable amperometric nitric oxide microsensor is described. It is based on Ni(chitin)2 mediators immobilized on a platinum, Nafion modified electrode. The detection of NO is based on the Ni(chitin)2 catalysis of NO oxidation at an anodic potential of +0.74V (vs. SCE). The catalytic peak current is linear for a NO concentration in the range of 8.5 108mol/L to 1.5 105mol/L, with a correlation coefficient of 0.9992. The detection limit of the microsensor is 5.0 108mol/L. It is suitable for the direct measurement of NO in biological systems.