Experiments were performed to examine Cd removal from waste water by sulfide precipitation using Na2S. It was shown that Cd is precipitated via two reaction paths: direct CdS precipitation, and indirect CdS precipitation through Cd(OH)(2) due to hydrolysis of Na2S. In order to realize suitable operation conditions, a dynamic model was built based oil the experimental results. Modeling results were in good agreement with experimental results. Furthermore, a pH control method for Cd precipitation and prevention of redissolution of Cd was proposed.