Abstract: The present work focused on the influence of NH4+ on the high affinity transport system(HATS) for K+.Hydroponic experiments were carried out to study the uptake kinetics of high affinity transport system for K+ by rice and soybean seedlings,and of their response to NH4+.The results indicated that the effect of NH4+ on Vmax of K+ uptake in rice was significantly lower than that in soybean.The influence of NH4+ on the values of Km of both two tested crops was neglected;indicating effects of NH4+ on K+ uptake are mainly attributed to its influence on the quantity of potassium carriers located at the cell membrane instead of on the affinity of the uptake sites for K+.