Adsorption reactions of aluminum on Na-montmorillonite have been studied in the temperature range of 293.15K-338.15K, and at initial pH of Al solution of 2, 3, 4, respectively.The effects of pH and temperature on the adsorption isotherm are discussed on the basis of experimental results.H⁺ adsorption on the clay edges, OH^- adsorption and the degree of hydrolysis of Al³⁺ adsorbed on the clay surface are estimated.The adsorption mechanism of trivalent ions with clay is also discussed.