Reduction of sodium nitrate solution by lead drops with wet-ballmilling is studied in order to remove concentrated NO3-from wastewater. Metal oxides forming on the lead drops surfaces in a ballmill reactor was continuously removed by inter-ball contacting. In the 5-80 degrees C temperature range, initial concentration of NaNO3 0.05-0.1 M, and ballmill rotation speed, omega, 80-180 rpm, NO3- is rapidly reduced to NO2(-), then slowly to N2 and NH3. NO3- is reduced to NO2- 32-100% in 10 h, but the reduction rate of NO2- is very slow, so the maximum percentages of N-2 and NH3 from NO2- are only 6 and 10 %, respectively. Above 40 degrees C, NO3- is reduced under zero-order reaction and NO2- is formed corresponding to the reduction stoichiometry. The reduction rate is proportional to omega(1/2) [rpm(1/2)], and the apparent activation energy is 27.5 kJ.mol(-1), but independent of the NO3- concentration. These results suggest that the rate determining step is the peeling of PbO layers on the particle surface. Below 25 degrees C, the reduction rate decreases with reaction time as the surface is not covered completely with PbO due to the lowering of the rate.