This study suggests that calcium oxalate monohydrate over Juniperus monosperma bark is an ion-exchangeable site for cadmium adsorption on the basis of its cadmium adsorption behavior and surface characterization. Cadmium adsorption behavior showed that juniper bark had a higher cadmium adsorption capacity (84.6 μmol Cd g.1 at pH 5) than juniper wood (32.0 μmol Cd g.1 at pH 5), and that the base-treatment improved the cadmium adsorption capacity of only juniper wood. This difference between juniper bark and wood might have originated from different cadmium binding sites. In calcium displacement, the cadmium uptake onto juniper bark was identical to the amount of calcium ions displaced, which indicated that calcium played an important role in cadmium adsorption onto juniper bark. X-ray diffraction (XRD) results gave evidence that only juniper bark contained the structure of calcium oxalate monohydrate. Furthermore, cadmium adsorption decreased the intensity of the characteristic XRD peaks for calcium oxalate monohydrate. In diffuse reflectance infrared Fourier transform (DRIFT) spectra, existence of oxalate on juniper bark was proven again and interpretation on IR band of carbonyl groups matched significantly the cadmium adsorption behavior.