During 1985-1990 we conducted 4 field experiments on N, P and K to ginseng on solis of Changbai County and Gongzhuling City. All the results showed that nitrogen retarded plant growth and decreased yield of ginseng mostly at 5% sigificance level and even to the level of 1% when the rate of N doubled. By successive study, we found that the nitrate reductase acitvity (NRA) of ginseng was so low that the NO₃ absorded could not be.reduced promptly and was accumulated in the tissues, and that, compared with control, the N, Si, Cu> Zn> Fe and Mn contents incrased in N fertilized ginseng tissues, P and such cations as Ca, Mg, K and Na decreased, and the respiration rate of ginseng shoot accelerated (44.8% over control) by N top dressing. These have ever been described as N toxicity in literature. In this paper we tentatively refer to this physiological toxicity as ‘N excess',which is caused by the fact that the N supply is too much to transfer instantly by low NRA.