Adsorption and complexation phenomena have been investigated in the ternary system Cu(II)-fulvic acidkaolinite. The reactions were followed by measuring (a) the concentration of exchanged protons, (b) the free copper concentration using a copper ion selective electrode, and (c) the total dissolved copper concentration by atomic absorption spectrophotometry. Fulvic acid concentrations have been determined by UV absorption. The results showed that the fulvic acid adsorption on the kaolinite surface follows a Langmuir isotherm in the concentration range studied, while the copper adsorption follows Freundlich’s law. Adsorbed fulvic material leads to an increase in the total quantity of adsorbed Cu(II) on kaolinite, when systems containing equal free copper ion concentrations are compared. This additional adsorbed Cu(II) plays a rather minor role in the total adsorption of Cu(II). A mathematical model is proposed for the interpretation of the data.