The adsorption of nitrate ions by three variable charge soils and four constant charge soils of China were measured under different pH, co-existing Cl^- or S0₄^2- and accompanying K⁺,Na⁺ or Ca²⁺.The results showed that the amount of NOD adsorbed by soils decreased with increasing pH. For variable charge soils, the amount of adsorbed N0₃^- in different electrolytes decreased in the order Ca(N0₃)₂>KNO₃>NaNO₃>KN0₃+KCI>KN0₃+K₂SO₄.Within the range of 0.5 to 5 mmol L^-1 of NOD added, the adsorption can be described by the Langmuir equation satisfactorily, and the adsorption energy parameter(K) as calculated from the equation was similar in magnitude when different anions and rations co-existed. This implies that the adsorption of NO₃^- is mainly determined by electric force, which can not be changed by such factors as the type and the concentration of co-existing rations and anions. These factors can only influence the adsorption of nitrate through changing the surface properties, mainly the quantity of positive charge of the soil. However, the adsorption of nitrate by constant charge soils was a little higher in Ca(NO₃)₂ Solution than that in other electrolytes. The maximum amount of adsorption by these soils was only 1.5 mmol kg^-1,corresponding to about one tenth of the adsorbed N0₃^- by variable charge soils. For these constant charge soils, a negative adsorption of NO₃^- was usually observed at low concentrations.