Abstract: Changes of plasma membrane potential in young root tip cells of rice(Oryza Sativa L),Yang dao 6(Indica) were monitored using glass microelectrodes during the uptake of different concentrations of NO3-(0.01,0.02,0.1,0.2,0.5,1.0 and 2.0(mmol/L),respectively).The results were as follows: 1) The absorption of NO3- by the roots made membrane potential depolarized and then repolarized.Furthermore,hyperpolarization was found in some root cells.Within concentration of 0.011(mmol/L) NO3-,the magnitude of depolarization increased with the increasing of NO3- concentrations and there existed a significant difference in the size of depolarization between treatments(P 0.05).The average depolarization,for example,was only 3.8 mV under the concentrations of 0.01(mmol/L) NO3- but it reached the largest size,i.e.,40.2mV in 0.5(mmol/L) NO3-.The magnitude of depolariztion declined with the further increasing of NO3- from 12(mmol/L). The course of NO3- uptake by rice roots reflected by the response of depolarization of plasma membrane potential to external NO3- concentrations exhibited Michaelis-Menten kinetics.2) Partial and complete repolarizations after depolariztion were found during the uptake of NO3-.Hyperpolarization also displayed two modes: one was the hyperpolarization followed by a slow repolarization and the other was a big hyperpolarization after a small depolarization.3) The response of the membrane potential to NO3- in rice roots was inhibited by PGO,an inhibitor of NO3- transporter,showing that the transport through plasma membrane was completely finished by the NO3- transporters in rice roots.4) Ca2+ mainly caused hyperpolarization in rice roots that precultured in CaSO4 solution.