Intracellular measurement of nitrate activity in leaf cells of Chinese cabbage in vivo using double barreled nitrate selective microelectrode was reported for the first time in China These microelectrodes showed a typical log linear response to nitrate concentration from 100 mol m^-3 to 0.01mol m^-3 with a slope of 48~ 58 mV and the nitrate act ivity detectable was very low The microelectrode was characterized by a high selectivity and sensitivity of ion and a good economy compared with other intracellular measurements In addition, the in vivo method is better than the chemical analysis of the samples The detected results showed that nitrate activity in leaf cell of Chinese cabbage induced with 5 mol m^-3 nitrate for 48h fell into two different populat ions, i e 0.24 mol m^-3~10 mol m^-3 in cytosol and 20 mol m^-3~110 mol m^-3 in vacuole Since vacuolar volume accounts for 90% of a whole cell, most of the nitrate in plants is stored in vacuoles And, thus it is of great importance to study the remobilization of the nitrate in vacuoles both in increasing nitrogen use efficiency and in decreasing the nitrate content of vegetables.