To investigate effect of sequence of sulfate addition on adsorption of Cu²⁺ by soils, samples of variable charge soils (Ali-Haplic Acrisol from Jinxian, Rhodic from Xuwen and Hyper-Rhodic from Kunming), constant charge soils (Haplic Luvisol from Nanjing and Brown soil from Weihai), geothite and kaolinite were used in the experiment. All the samples, except kaolinite, were treated with electrodialysis. Copper ion was spiked at a rate of 1 cmol L^-1, and sulfate at a rate of 0.1 cmol L^-1 and 1 cmol L^-1, separately. The experiment was designed to have three treatments in sequence, that is, Treatment 1: addition of copper nitrate, stand, vibration and addition of sulfate; Treatment 2: addition of copper sulfate and nitrate the same time, stand and vibration; and Treatment 3: addition of sulfate, stand, vibration and addition of copper nitration. All the samples were treated to keep copper ions and sulfate the same in concentration in the suspensions before vibration in the end. Soil pH of the samples was measured with glass electrodes, and copper ions measured with Atomic Adsorption Spectrometry. Results show that the effect of sequence of sulfate addition on Cu² adsorption by soils varied from soil to soil different in surface charge properties. For constant charge soils, the sequence of sulfate addition did not have much effect on Cu² adsorption. On the other hand, among the three treatments, when pH was kept the same, variable charge soils, kaolinite and goethite in Treatment 2 were the highest in Cu² adsorption rate. For Ali-Haplic Acrisol, the samples in Treatment 3 were higher than those in Treatment 1 in Cu² adsorption rate. For Hyper-Rhodic Ferrasol, Rhodic Ferrasol, kaolinite and geothite, the effect was just the opposite to that on Ali-Haplic Acrisol when they were under the same condition. No matter on what samples, application rate of sulfate did not have any effect on the order of the treatments in Cu² adsorption rate, and a similar phenomenon was observed when Hyper-Rhodic Ferrasol was deprived some of its organic matter. It is generally accepted that anions may affect soil adsorption of coexisting cations in three ways: (1) ion strength; (2) specific adsorption; (3) ion pairing. As in the end, the anions and cations in the suspension are the same in type and concentration, the effect of ion strength on Cu² adsorption should not have any difference. Although specific adsorption of sulfate will lead to release of hydroxyl, thus altering Cu² adsorption electrochemical properties of the suspension, the comparison of the treatments in was done under the condition that the suspensions were the same in pH. In this experiment, the only factor causing differences between the soils in Cu² adsorption might be the complexing reaction of sulfate and copper ions with soil surface. After careful consideration of the findings in the experiment and the differences in surface electrochemical properties between the soils used in the experiment, it can be concluded that the causes of the differences between the soils in Cu² adsorption should be the complexing reaction of copper ions and sulfate with soil sulfate, and the difference between variable charge soils and constant charge soils in surface charge properties.