There have been many papers reported on low use efficiency of chemical N fertilizer and its loss leading to environmental pollution but very few ones are found to have advanced achievements.High contents of nitrate in some plants, especially in vegetables and fruits, decrease significantly the qualities of these plants, thus becoming one of the limiting factors for the exporting of the products.Studies on the mechanisms and ways to high use efficiency of N in plant itself have become one of the issues in plant N nutrition in the last a few years.Vacuoles occupy about 90% of the total volume in matured cells of plants and the concentrations of nitrate in vacuoles and cytosol are normally 30~50 mol m^-3 and 3~5 mol m^-3, respectively.Therefore, it is one of the ways to increase the N use efficiency and decrease the contents of nitrate in plants that the nitrate in vacuoles are remobilized and reutilized.The present paper reviews the main studies on the behavior of nitrate in vacuoles.The author proposes in the first time that there should be some close relat ionships between the influx and efflux of nitrate though tonoplasts and N use efficiency in plants.The author also on purpose initiates the research work of this field in China by exposing some issues to be considered.