This paper reports an amperometric nitric oxide (NO) microsensor based on a cone-shaped nanopore-platinized Pt working electrode. The senor was fabricated using the following procedure: (1) a parent nanodisk electrode was prepared by polishing an etched Pt wire (radius = 12.5 μm; dimension of etched tip end point <10 nm) embedded in a glass capillary, (2) the nanodisk Pt was further etched to produce a nanopore (pore opening radius <1 μm; pore depth ∼30 μm), (3) the Pt base surface in the nanopore electrode was platinized electrochemically to improve the sensor sensitivity, and (4) silanization and further modification with the electropolymerized polymeric film [poly(5-amino-1-naphthol)] on the nanoporeplatinized Pt electrode were carried out to obtain the sensor selectivity to NO. The analytical performance of the sensor was characterized. For example, a sensor with a pore opening radius of 797 nm exhibited a decent linear dynamic range (at least for 0.2-1.8 μM), detection limit of < ∼32 nM, response time (t90%) of < ∼5 s, and sensitivity of 6.5 ± 0.02 pA/nM. This sensor was used successfully as a NO-selective probe tip in scanning electrochemical microscopy (SECM) to obtain a two-dimensional image of the local NO concentrations for an inlaid NO-emitting microdisk film (radius = 12.5 μm) on a glass substrate.