A novel amperometric sensor for the determination of nitric oxide was developed by coating polythionine / nafion on a glassy carbon electrode. This sensor exhibited a great enhancement to the oxidation of nitric oxide. The oxidation peak currents were linear to the concentration of nitric oxide over the wide range from 3.6×10-7 to 6.8×10-5 mol. L-1, and the detection limit was 7.2×10-8 mol. L-1. Experimental results showed that this nitric oxide sensor possessed excellent selectivity and longer stability. NO releasing from rat kidney was monitored by this sensor.