The chemical stability of nitrate and its reduction into nitrous oxide or nitrogen gases as end products was theoretically studied using Nernst's equation , under different sets of Eh (0,200 and 400mv) and pH (5, 7 and 9) comparable to those of soils. Calculations using Nernst's equation and published data on ion activities and redox potential declared that nitrate stability is very sensitive to little changes in soil reaction (pH) and/or redox (Eh) values. Nitrate transformation into N₂O and N₂ goes easier at low than at high pH and Eh values.  A decrease of pH by one unit increases the activity of the produced N₂O and N₂ by 10¹⁰ and 10¹² folds, respectively. Also, their activities increased by 10¹¹ and 10¹⁶ folds due to decreasing Eh value by 100 millivolts. In addition, when increasing the nitrate activity by 10 folds, the activity of any of the two gases increases by 100 folds. Among the two gases, N₂ production was more sensitive than N₂O production towards the changes in pH and Eh values. Similar trends were found by other workers as to the effect of pH and Eh on nitrate reductions. Therefore, it is expected that small changes in soil pH and/or Eh can cause important chemical reduction of the applied nitrate fertilizers especially under extensive cropping systems to form N₂O gas which shares in the environmental problems through its reaction with the ozone layer.