Due to the inhibited nitrification in the bulk soil of lowland rice field,researches on nitrogen nutrition of rice mainly focus more on ammonium than nitrate.In fact,the roots of rice can excrete O₂ to surrounding soil and this can convert NH₄⁺ to NO₃^- in the process of nitrification at root surface or in rhizosphere.Rice roots are actually always exposed in a mixture of NH₄⁺ and NO₃^- although the predominant species of mineral nitrogen in the soil collected from the lowland rice field is ammonium.This paper reviews the nitrification process in the rhizosphere of rice,and discussed the stimulation of nitrate on the absorption and utilization of ammonium by rice from both the uptake rate and root growth.The pathways involved in the local and sys temic responses to NO₃^- supply were also discussed.In terms of the local stimulation by NO₃^- on the lateral roots,the nutritional function and signal function of NO₃^- were clarified in details from its effect on carbohydrate,amino acid,phytohormones.Finally some issues on nitrate nutrition of rice are proposed to be studied further.