The present study developed a microdevice for reduction of nitrate ion made of zinc or copper with the purpose of reducing the impact on the environment. The performance was evaluated by reduction of nitrate ion in a nitric acid aqueous solution of 10(-2) mmol/L (10(-2) mol/m(3)) as a sample. Nitrate ion was reduced to nitrite ion using a microdevice made of zinc, which is environmentally-friendly reductive reagent. The behavior at shorter contact time to zinc was considered to come from the adsorption process of nitrate ion to zinc before a reduction process. However, the reduction eficiency of nitrate ion remained 12.1% at 0.067 mu L/s (6.7 x 10(-11) m(3)/s), which corresponded to a longer contact time to zinc of 120.4 s. Moreover, bonding between the zinc and polydimethylsiloxane ( PDMS) substrates did not last long. On the other hand, nitrate ion was reduced to nitrite ion using a microdevice made of copper, which was made by a fabrication method enabling seamless bonding. The reduction eficiency of nitrate ion reached 79.4% at 0.083 mu L/s (8.3 x 10(-11) m(3)/s) in the microdevice with the single-layered structure, and 62.0% at 0.25 mu L/s (2.5 x 10(-10) m(3)/s) in the microdevice with the four-layered structures. The microdevice made of copper showed about 6 times the reductive ability for nitrate ion compared with that made of zinc. Also, the flow rate range of nitric acid aqueous solution using the microdevice with the four-layered structure was larger. The microdevice with the four-layered structure having larger flow contributed to improving versatility. Furthermore, the internal volume in the microdevice was only 10.5 mu L (1.05x10(-8) m(3)), and thus the sample volume in the microdevice was obviously much smaller than that of 200 mu L (2.0 x 10(-7) m(3)) in the flow injection analysis (FIA) method. Therefore, using a microdevice might keep the impact of copper on the environment to a minimum.