Abstract: Changes of the plasma membrane potential on root tips of two rice(Oryza sativa L)cultivars,i.e.,Wuyujing 3(Japonica) and Yangdao 6(Indica) were monitored using microelectrodes under different concentrations of NH4+(0.025,0.05,0.1,0.5,1.0 and 1.5 mmol/L).The results were as follows: NH4+ uptake by the roots made plasma membrane(potential) depolarized;however,depolarization to the certain degree,it appeared the partial repolarization and hyperpolarization in some parts of rice roots during the absorption of NH4+.The magnitude of depolarization increased with the increasing of NH4+ concentrations until a stable state.The course of NH4+ uptake process conformed to Michaelis-Menten (kinetics).The two rice cultivars had different depolarization modes in which the average values depolarized were 16.5 mV(Wuyujing3) and 22.6mV(Yangdao 6).Under low concentration of NH4+(1mmol/L),with its higher average level of depolarization(17.5mV),Yangdao 6 was more sensitive to NH4+ being higher compared to Wuyujing 3(10.7 mV),and there existed a significant difference in the size of depolarization between these two cultivars(p0.05).This suggested that Yangdao 6 had the stronger capability to take up NH4+ than Wuyujing 3.The results obtained in this experiment were consistent with those of kinetics of NH4+ influx.