Kinetic and thermodynamic characteristics of cadmium adsorption on humic acid were studied using ion-selective electrode.Results show that the characteristics of cadmium adsorption on humic acid differed with the medium pH at the adsorption data were best described by Freundlish equation at pH 3.0~3.5 and by Langmuir equation at pH 4.0~6.5,respectively. Significant correlations existed between cadmium adsorption amounts and the medium pH at the range of pH 3.00~6.50 under the experimental conditions. The increase of temperature resulted in a decrease of the cadmium adsorption amount on humic acid, suggesting a heat-release reaction between humic acid and cadmiumions. The adsorption heat was pH-relevant with an increased adsorption heat at higher medium pH. The adsorption forces of cadmium on humic acid varied substantially with the change of medium pH,with ligand exchange being dominating at pH 6.5 and hydrogen bond and dipole force being the main forces at pH 5.5. The adsorption processes involved partly electrostatic force without the release of hydrogenions. The logarithm of the adsorption distribution coefficient(log K_f)positively correlated with the medium pH at low cadmium concentration. An initial fast reaction stage followed by as slow reaction between humic acid and cadmium ions were observed and it took at least 500 min for the reaction equilibrium to be established. The reaction rates were accelerated with the increase of medium pH and the adsorption kinetics were best described by Elovich equation followed by double-constant equation.